Power Supplies

The inexpensive standard 60 Hz PSC motors most
have Class B insulation and don't have the ruggedness
to long survive in a variable frequency drive or being driven
by a noisy waveform . When they hum to any great extent ,
they are being damaged by magnetostriction and that is what is being heard as the audio signature of the effect .

So for my purposes I am going to stay with 60 Hz , that is simply a given , and vary the voltage , letting the inherent
power feedback of a PSC motor driving an external quadratic load provide *some* stability to the speed , augmenting that power feedback from the driven load with additional inherent power feedback from a quadratic load which is an ever present parasitic load perhaps amounting to 20% of the
total output realizable from the motor . I am definitely going to use this approach of passive closed loop regulation before
going further to any active closed loop regulation by digital
tachometer and error signal processing which effects active modulation of the power to the motor . Using passive feedback is as easy as putting a quadratic load on a motor ,
whereupon the speed response of the motor is immediately very different from a completely unloaded motor with a bare shaft sitting in a test cradle spinning away freely and driving nothing .

Consider the following scenario as in illustration of my idea for passive closed loop inherent speed regulation. A squirrel cage blower wheel is a quadratic load which can be varied simply by opening up or closing off the intake airflow
to increase or decrease the loading the wheel places on the
driving motor . Suppose you have a blower wheel whose
inside diameter is just a fraction of an inch larger than the case diameter of a double shaft motor which is top mounted vertically with its lower end hanging in free air . And you invert the blower wheel on the lower shaft so that the motor
body slips inside the blower wheel for half the length of the motor . Now most of the intake area for the wheel has been obstructed by the motor body so the wheel has been greatly unloaded as compared with its normal free air loading , and
as a bonus some very effective cooling airflow has been added to the motor , even at low speed operation because
the wheel has to pull nearly all its airflow through the openings in the endshields of the motor . The effect of this
parasitic quadratic load on the motor may be further augmented very easily by attaching small permanent magnets on opposite sides of the endshield which is
within the blower wheel , so that the disc which is the backing plate for the wheel is affected by eddy current loads
induced by the influence of the static fields from the permanent magnets . The intensity of this eddy current braking could be adjusted simply by raising or lowering
the mounting position of the wheel on the lower shaft ,
to increase or decrease the air gap between the rotating disc and the magnets on the endshield of the motor .

By this scheme there is provided both low speed cooling for the motor and an adjustable quadratic load which conveys
inherent speed regulation to the motor at a given voltage .

Has the term " elegant " come up somewhere in this
discussion ?

Now what were some folks saying about " engineering " ......

Hmmmmm ?

Rosco breathes on fingernails and buffs them against his collar

Need a bigger chair about now , something more
befitting an intellect of such stature

What say you , fellow gentlemen and scholars

Is this good or is this good ?

Oh contrare .

It is a Beckett wheel # F120-42S precision balanced
for 6400 rpm duty , but I'll never run it past 1200 rpm
and it is dead silent and vibration free .

http://www.beckettair.com/fergas-wheels/Fergas-Single-specs....

The clearance between the motor case and the inside tips
of the turbine blades is about 5 mm which is plenty .
A fat O-ring glued to the motor case could even close that gap nearly completely if necessary .

An even closer clearance could be gotten with a # F115-42S
but I have the slightly larger wheel already on hand .

BTW ,

I'm a rambling wreck from Georgia Tech ........

And ........

And .....

How does the rest of that song go ?


I'm A Rambling Wreck


I'm a Ramblin' Wreck from Georgia Tech and a hell of an engineer,
A helluva, helluva, helluva, helluva, hell of an engineer.
Like all the jolly good fellows, I drink my whiskey clear.
I'm a Ramblin' Wreck from Georgia Tech and a hell of an engineer.
Oh, if I had a daughter, sir, I'd dress her in White and Gold,
And put her on the campus, to cheer the brave and bold.
But if I had a son, sir, I'll tell you what he'd do.
He would yell, "To Hell with Georgia," like his daddy used to do.

Oh! I wish I had a barrel of rum and sugar three thousand pounds,
A college bell to put it in and a clapper to stir it round.
I'd drink to all good fellows who come from far and near.
I'm a ramblin', gamblin', hell of an engineer.




[Edited on 5-2-2006 by Rosco Bodine]

Quote:

Has the term " elegant " come up somewhere in this discussion ? Now what were some folks saying about " engineering " ...... Hmmmmm ? Rosco breathes on fingernails and buffs them against his collar Need a bigger chair about now , something more befitting an intellect of such stature What say you , fellow gentlemen and scholars Is this good or is this good ?

If this were a computer or electronics group/board you'd find the view from your position nailed upside-down on the dartboard very enthralling

My chemistry knowledge is mostly 40 years out-of-date and I humbly acknowledge the work many people here put into research. For things with wires, I give PhDs headaches because I'm right more often than they are.

[Edited on 5-2-2006 by densest]

Quote:

If this were a computer or electronics group/board you'd find the view from your position nailed upside-down on the dartboard very enthralling

If you chillun don't respect your elders , then how can
you ever get beyond just being apprentices
I'm a hardware hacker from way back .

I am intrigued by the regulated AC power supply you have described , and if the schematic gives me a headache I'll
probably stick with the components I already have in transit
for the prototype . There is a lot of the KISS philosophy applied to whatever I do , and I know there are other ways
maybe better ways in terms of absolutes . But I also know
it is possible to overdesign something simple and make something more difficult than it has to be . So I am trying to keep this as simple as possible without really compromising
function which is desired to be only very damn good .......
not perfect

[Edited on 6-2-2006 by Rosco Bodine]

Here is another revision to my circuit attached ,
which does away with the dual pots . There will
likely be further revision to isolate the high voltage
mosfet gate driver circuit from the control pot ,
and use regular TTL level through an optocoupler ,
perhaps using a vactrol type optocoupler as I mentioned
in describing earlier thoughts here about this project .
It just mades for a safer panel to have low level on a
control pot , and avoid line level signal if there is any
way to manage that , which can likely be arranged
with a few more components .......might as well
do the job right and supply a TTL level input capability
which will be useful for other things too . That's what's next
if anyone wonders where I'm going with this .

Anyway , please take alook at this revision and holler if any
defect is spotted .

Ermmm, why did you draw two zeners? What happens when supply voltage exceeds Vf and line voltage appears on the gate? Either smoke, or you get a maximum voltage drop of whatever the zener is...

Speaking of diodes, you even draw the MOSFETs explicitly with intrinsic body diodes -- what are the external diodes for? Most MOSFETs have reasonably rated body diodes.

In case the AC load is disconnected, there should be a "fixed value idle current resistor" in that place, too.

The FWB trick looks like it will work.

BTW, your drawing is nice and neat and square. Although arc wire crossings and really really long resistors went out of style in the 1960s.

Tim

I'm not source following you there .....Vf where ?

Quote:

BTW, your drawing is nice and neat and square. Although arc wire crossings and really really long resistors went out of style in the 1960s.

I actually like to see and draw the overpassing conductors
with the semicircle , because it shows the layering of the
flyover , ( or under ) conductors so that if you are visualizing
tilting a " panel " of the circuit , imaginary connecting wires
are kept from imaginary snags on other conductors and components It helps visualizing the hookup points and conductor paths for the board especially when the circuit is
not printed , but manually wired on perf board .

[Edited on 7-2-2006 by Rosco Bodine]

@ Twospoons

Thanks for catching that .

You are absolutely right and I am looking at it ,
because I sure as hell missed it completely or
thought it " back to back " and didn't draw it .

What I need there is an ordinary diode back to back in series with that Zener . I will correct the drawing .

@densest

I know DC gives the best performance . There is nothing
experimental about that approach , and what I am about
here is sort of like star trek , you know going where no
one has gone before , giving the lowly PSC motor made
cheaply by the gazillions something different to do where
it is better than the shaded pole motors used already in
the application . As for the rheostat , I have several of them
and its been there , done that , and know the limitations .
I'm on the right track I think and if not , well then the
experimental prototype will be a learning experience .

@ Twospoons

The attached revision of the schematic shows the corrected
diode protection for the gates . Thanks again for spotting the missing diodes .

@ 12AX7

I take it that both you and Twospoons were seeing the same
missing blocking diode there and that is what you were meaning about Vf appearing at the gate ? Thanks for hollering .....I got it , fixed it too

[Edited on 7-2-2006 by Rosco Bodine]

LOL , I'm dying here because I know seeing a MOSFET
upside down from its usual orientation as a " switching "
device is like trying to ride a bicycle backwards . I am having the same problem with the visualization , like
holding a rifle on the shoulder aimed at a target behind the back and aiming by lining up the sights with a shaving mirror held at arms length . You have to think it through like
looking through a telescope without a terrestrial inverter ,
because everything tries to move the " wrong way " as you
are visualizing it with a mind conditioned to the opposite
configuration

Because I saw what you were meaning to point out ,
even though you described its actual location flipped
180 degrees from where the defect was
This " source follower " configuration makes me crosseyed too

LOL ...I do love my damn diodes don't I !
But there's nothing like a cathode rejuvenator on
a cold winter night If the girls are squeamish
when you ask them to Thevinize it , you sometimes
have to settle for a quick Kirchoff

They are pretty aren't they ? Watch out now ,
or people will think you have the hots for a MOSFET
Isolated oversized cases too , long beautiful legs
all the way up to her ass ....sweet

70 Nm + or - 10 Nm mounting torque , and the cases
are flat both sides so they can be sandwiched between
two heatsinks if you like .

Maybe google 'em or check eBay , there's a few around .

Meh, TO-247 isn't very sexy, it has sharp masculine corners if anything. A pair of TO-3's side-by-side would be more interesting.

But anyway.

The single source-gate zener diode is forward biased if the gate is less than the source, keeping the gate above -0.7V. Likewise it is reverse-biased (zener clamp), limiting gate to below say, 12V, for a 12V zener. Considering the transconductance, you could easily get away with a 6V zener. This and this alone is sufficient and there is no need for any more diodes.

The 2SK1837 is more than stocky enough to withstand reverse current, so external reverse diodes are not necessary. Diodes are not required for the "idle current" resistors, which themselves are not necessary either (when the output is turned down, current is low, so dissipation is low -- for a resistive load, maximum dissipation takes place at *half* voltage output!).

Study it more and you'll see it.

Tim

Quote:

Originally posted by 12AX7 Meh, TO-247 isn't very sexy, it has sharp masculine corners if anything. A pair of TO-3's side-by-side would be more interesting. But anyway. The single source-gate zener diode is forward biased if the gate is less than the source, keeping the gate above -0.7V. Likewise it is reverse-biased (zener clamp), limiting gate to below say, 12V, for a 12V zener. Considering the transconductance, you could easily get away with a 6V zener. This and this alone is sufficient and there is no need for any more diodes. The 2SK1837 is more than stocky enough to withstand reverse current, so external reverse diodes are not necessary. Diodes are not required for the "idle current" resistors, which themselves are not necessary either (when the output is turned down, current is low, so dissipation is low -- for a resistive load, maximum dissipation takes place at *half* voltage output!). Study it more and you'll see it. Tim

I looked at the data sheet and a dozen others
before choosing this particular MOSFET . I assumed
the +2 to +3 volt threshold above source would hold
true whether the load was top driven from the source
lead above as in a source follower circuit , or if the load
was top tied to a supply rail and switched from below
by the drain lead through the Mosfet in the usual switch mode where the source is on the negative rail .
The turnon voltage is the same value turnon voltage no matter where the mosfet is located in series with the load .

So the source can only rise to within 2 to 3 volts lower
than the gate voltage applied to the mosfet acting as a source follower . If the potential on the source tries
to rise higher , the Mosfet is no longer " saturated "
as a switch , but becomes semiconducting and operates
" active region " or " linear " as a voltage controlled variable resistor to regulate the voltage on the source at the 2 to 3 volts below the voltage at the gate .

I don't see how an external zener of higher voltage than that 2 to 3 volts would interfere at all with that normal
excursion of the source voltage which derives from the internal mosfet components providing the source following effect . It's like you are saying the source can rise no higher than the drop across the zener when it is in zener conduction , and applying that to a scenario where the zener is not in zener conduction , and where it wouldn't matter in either case anyway . All the source will do is rise to within 2 to 3 volts less than the voltage on the gate , where it stays , regardless of a zener which
has dropped out of zener conduction way before the
source voltage has risen that near to the gate voltage .

It seems you are looking at the diodes as providing some
sort of active biasing which is either simply not there or I don't recognize it yet . All the single zener from gate to source does is limit the gate from going over 15 volts
with respect to the source , when a third of that would be more than enougn to saturate the Mosfet , so all the single zener does is clamp any excess voltage which might appear as a transient on the gate . And if the single zener was in normal forward conduction , it is supplied from the source whose potential cannot be
higher by the 2 to 3 volts plus the .7 volt drop across
the diode , for the Mosfet as it were to " self - bias "
its own gate from what voltage is on the source .

Any forward biasing of the mosfet gate is going to have to
be routed from the rails on the drain side of that Mosfet .

What you were saying above about not needing the reverse
current protection on gate to drain versus my assertion earlier that the mosfet would be destroyed by the same reverse voltage as is stated for gate to source ..... I admit that I am uncertain of this and you could be correct . The manufacturer doesn't specify any limitation for the gate to drain as they do for gate to source and here I assumed that because N channel Mosfets are unipolar devices having a single carrier channel from source to drain , that the relative
vulnerability of either end of that channel to overvoltage
would be the same . I have read somewhere that N channel
mosfets have a somewhat ambiguous " polarity " with regards to the matter of drain and source , and will happily
pass AC under certain conditions , and I'm not even certain that is true , but adding these things together it just made sense to me that the gate to source allowable voltages likely
applied equally to the gate to drain . Not knowing for sure ,
I choose to add the diodes which shouldn't hurt a thing if
they aren't needed , but will protect the Mosfet if they
should be needed . When I draw the final circuit I will
have the diode protection on both the gate to drain and the gate to source , for my own peace of mind . It may be sort
of like seatbelts and airbags , or it may be like two seatbelts
when one would do . But either way , the thing is covered .
If anybody else wants to omit the clipping filters they are welcome , but I am putting them in the one I build just to be sure

[Edited on 8-2-2006 by Rosco Bodine]

Here is the latest revision . The changes are to
make the biasing more assertive so that the
circuit will have better performance near the
zero crossing and will also deliver closer to
full voltage at the maximum setting . A better
output waveform should result , having
less noise and less heat from the mosfets .

An upper voltage limit setting has been added
in order to allow full control over defining the
response range of the Main Voltage adjustment
which is the " speed control " .

The power resistors for idle current to the motor
have been deleted to simplify the configuration ,
and large enough heatsinks for the mosfets will
manage any heat dissipation when the motor
is at idle speed .

A power switch and power indicator lamp are
shown on this new schematic . A value for the
capacitor and its charging current limiter resistor
have not yet been calculated . The idea is that
this capacitor will charge nearly to the peak 170 volts
on the first half cycle , and hold that higher voltage
across the divider string of the control pots so
that the V ref to the source follower stays at a
more constant and higher voltage and supplies
this steady high level signal to the gate of the
source followers , so that they switch on suddenly
and in saturation at the zero crossing , reducing
that part of the cycle where they would otherwise
be operating unnecesarily in a linear mode , if
following always 3 to 5 volts below a gate signal
varying synchronously with the line voltage .
Using this scenario the mosfets will switch on
in saturation at the zero cross and stay in saturation
until their sources attain a voltage 3 to 5 volts
below the constant V ref being supplied their gates ,
which will reduce the heat dissipation of the mosfets
by allowing them to operate more efficiently during
that earlier part of the cycle where they can .

Any suggestions / justifications for the value of the
capacitor , limiter resistor , and the gate resistor values
is welcome .

[Edited on 9-2-2006 by Rosco Bodine]

Just looking at that circuit Rosco I would be very nervous about parasitic oscillation when I flick the switch. As previously mentioned the input impedence to the FET's needs to be as low as possible to prevent this. With the bias resistor configuration you have there appears to ensure an unfavourable situation for stable operation although the DC outlook looks fine. My immediate thought is to keep the rectifier but have variable voltage regulators to bias the FETs, having a much lower output impedance, basically use that circuit as it is with common emittor transistor or darlington driver configuration, biased in class AB (about 10mA in class A) in front of the resistor devidors. I would try 1,5K for the gate resistors.
The driver transistors would dissipate about 2W on idle and may need a small heatsink.

It's very interesting to see how the circuit has evolved, makes me wonder what the very first lightbulb looked like

The idle voltage for the motor is always going to exceed
the voltage of the zener regulation on the gates , so in reality each mosfet has its own local zener regulated power supply directly on its gate .

The gate input impedance of a mosfet is so high that it makes little difference what series gate resistance there may be added externally , the " felt impedance " of that entire signal lead will be several megohms to tens of megohms . A sufficient resistor value should be used to
prevent any overcurrent damage to the gate protection
circuitry in the event of an abnormal signal condition ,
but even a 1 Mohm or more gate resistor can be used
if wished to bias the high impedance gate . I am looking at 220K to 470K as candidate gate resistors . You have to consider how much decrease of the level of V ref will
be caused by the current through the zener from
gate to source , ( or alternately from gate to drain ) which will appear as a load tap on the divider string composed of the potentiometers . The value of the gate series resistor must then be pretty high to prevent undue voltage drop on the selected V ref . by putting too much load on the divider string setting that reference voltage . At the reference voltage tap on the Main v. adj . potentiometer appears a load
which consists of the sum of the two currents required to
bias the zener at the gate with the current limited by
the series gate resistor . The mosfet itself is essentially
invisible as a load on the biasing circuit , since its gate
requires virtually no current at all , but is biased essentially by the voltage alone across the zener .

Acting as a source follower with the source voltage rising to meet the absolute V ref. , when the zener drops out
of zener conduction , it will unload the signal lead of the zener current and a slight positive rise in the Gate voltage will reenforce the rise of the Source voltage
towards the selected V ref. So the feedback here is
in the proper positive direction to supply switching hysteresis , and noise immunity as is desired .

I think it's a good circuit , but time will tell , and the proof is in the pudding . I've designed and built way more complex stuff than this which works fine , so I have confidence it will work as intended , and the
parasitics be damned With intelligent lead routing ,
or even a Faraday cage , steel box for the circuit if
necessary , and this baby should work .

The one place I can see adding a Darlington pair . or really just a simple NPN emitter follower , something like a 2N2222 might be fine , is to current amplify the V ref signal from the wiper on the center pot to the tied together gate resistors
for the mosfets . The collector of the NPN would go to the
top end of the divider string composing the pots , the base lead would go to the wiper , and the emitter would go to the
tied together + feed ends of the gate biasing resistors . This
current amplification of V ref selected would prevent loading
of the divider string by the gate biasing resistors which could be much lower resistance value . Is this what you are suggesting to do ? Because I agree it would be better biasing and less susceptible to oscillation to current amplify the gate signal in such a way with a unity voltage gain one or two transistor current amplifier , the good old emitter follower . It seems excessive to have to dump 2 Watts from
a mosfet biasing amplifier . I'm looking at it and it really
depends on just how hot you want to run the gate bias resistors and the zeners . I'm thinking a tenth that 2 watts
would be plenty sufficent to get rock stable gate biasing ,
and I'd like to stick to signal circuits that require no heatsinking as if they were power devices

[Edited on 9-2-2006 by Rosco Bodine]

Thanks to froot for suggesting a lower impedance mosfet biasing , as has been mentioned before .

And thanks to 12AX7 for suggesting better placement
of capacitor charge current limit resistor .

The changes hoped to address these two matters are
shown in the attached revision of the schematic .

Do you gentlemen see any problem using an NPN emitter
follower the way I have it shown with the collector
tied to a 170 volt supply ? Ordinarily the reverse BE
breakdown voltage limit for the NPN might not allow this ,
but the ordinary diodes which I have straddling the mosfets
should be protective , so it is good they are there hmmm ?
HeHeHe .....
looks like they may be good for something after all
I guess it might be worth looking at all the other voltage
limits too , because I'm not sure this will work anyway .
This is a new one on me , so please speak freely .

Looking at CE Max V and thinking about the voltage allowable to be dropped across the collector to emitter for a
common NPN , I doubt any usual bipolar tansistor would survive even a fraction of the voltage encountered here .
But a high voltage Mosfet could , so what I will probably end up with here is using a high voltage rated signal mosfet in the place of the NPN , if the original biasing scheme really
needs this change involving a signal amplification intermediate stage , so the output mosfets can be
operated off a low impedance biasing scheme .

One can see a small perplexity here because this signal mosfet certainly can't be low impedance biased either , or else it may as well be omitted entirely and the main output power mosfets biased directly using V ref from the main pot .
Using an intermediate signal current amplifying mosfet
is also going to cost 3 to 5 volts drop in the maximum voltage output possible from the main power mosfets ,
but a lot of stability and noise immunity would be gotten
in return .

Using one Mosfet to drive the biasing of another Mosfet is
something like using Mosfets in a Darlington pair configuration , a thing which generally doesn't make a lot of sense when one of the things the high impedance input of a single mosfet is good for , is eliminating the need for a Darlington pair . But this scenario may be the exception where it actually does make sense to have one Mosfet used as a driver for 2 other mosfets . Can you say " fanout " ?
It's done in IC's all the time so why not

Guess we all know what is going to get substituted for the
NPN on the next drawing . Almost there !

Thanks for the help .







[Edited on 10-2-2006 by Rosco Bodine]

Are you familiar with the "TransZorb" product? It's a proof-by-existence that a bidirectional voltage limit gate-source is sufficient protection for the gates.

Is it a requirement that the parts count be very very low? There are a couple of things that could be done to drive the gates with a lower impedance voltage limited signal.

Are you aware that the circuit as presented will require a minimum of Vth + Vdiode across it - say 5-8 volts to operate? The motor will never run at full speed.

Here's a version which should be quite linear.

OK how do I upload a GIF?

[Edited on 10-2-2006 by densest]

@ Twospoons

It's going together anyway and when it works
you can take it up with the simulator authors
and let them figure out how to rewrite their
simulation software .

Edit / update

Sorry to be grumpy , this can be frustrating ,
and I do see why the simulation probably said it
won't work , and why it actually wouldn't work properly ,
though I disagree with the nature of the predicted
fault behavior .

I discovered this defect which I didn't see earlier , specific to
the idea of using a capacitor to bring up the voltage
to a constant level in the signal stage ......
the ground return path for that strategy is blocked in the bridge rectifier which charged the capacitor negative side . There is no DC " return path " for the circuit allowing the
increased voltage across itself to be referenced to line ,
The DC return path is blocked by the lower right diode in the bridge which originally allowed the capacitor to charge .
It's a subtle thing hiding there in plain sight , and it got by me .

So inserting the capacitor and trying to increase
the biasing voltage and hold it constant is a dog
that won't hunt , it just won't work the way I have
it drawn above . The bridge output has to be allowed
to rise and fall with the line voltage . That
synchronization is the only thing that gives the
positive voltage out from that bridge rectifier an
instantaneous value referenced to the line outside
the bridge .

So the capacitor idea is hereby deleted .
With it goes the hope of driving the mosfets harder
so that they acted as saturated switches through the
below peak voltage conduction times . It would be nice
if that idea had worked out , but it just doesn't work as
hoped . That is not to say the entire circuit lacks validity .
It just means the capacitor and the charging current limit
resistor have to be deleted .

The usefulness of a single mosfet source follower
signal current amplifier in the place of the NPN emitter
follower shown above is going to be explored and is shown
in the revised circuit attached .

This sorting out of the ideas and details which I have been
doing with fellow members help is leading to a valid circuit , even if it is a halting sort of progress where three steps forward reveals a snag causing one step backwards , it still produces a net gain of two steps in the forward direction ,
so progress is being made .

Ever since the revision of the circuit which departed from the dual pots and began using the bridge rectifier and single pots , I have had some reservation about the DC reference
to ground / return path to ground sorts of visualizations ,
looking at instantaneous AC values as a snapshot showing
a DC circuit behavior during a half cycle , and trying to keep it all straight when the inverted picture occurs for the next half cycle . It is maddening to try to mentally keep track of the
expected and intended behavior as inverted snapshots depicting the half cycles in reversal of polarities . I am in the right place for this ....Science Madness , and hopefully what will distill from this exercise is something useful .

In the interim I ask your forebearance with my smudges and
scribbles and revisions and corrections on this work in progress . And I thank you all for your criticsms and ideas
and suggestions , even simulations

Speaking of sims , try the corrected circuit attached here
on the sim and see if the results compute . This one
should fare better . Pay attention to the orientation of
all the mosfets as " source followers " , as they are absolutely inverted to their usual configuration when
used as switches . I estimate the voltage output of this
source follower bridge would be about 108 volts from
a 120 volt line .

[Edited on 10-2-2006 by Rosco Bodine]

Quote:

Here's a version which should be quite linear. OK how do I upload a GIF? [Edited on 10-2-2006 by densest]

Hi Rosco,
Re: strange schematic
The diodes make things look more complicated than they really are. The intent of the circuit is to bias Q3 dynamically to drop a fraction of the input line voltage as set by VR1.

R2, C1, and ZD1 make a sort-of-regulated power supply which can drive the gate of Q3 even with very little voltage across Q3 source->drain.

Q1 and Q2 form a differential pair with R3, R4, and R7 which subtracts the instantaneous voltage across the "rheostat" sampled by R5 and R6 from the instantaneous fraction of the line voltage sampled by R1 & VR1.

The output of the differential pair drives the output power transistor Q3. The circuit depends on the threshold voltage of Q3 being greater than the saturated voltage at the drain of Q2, set by the ratio R3 parallel R4 vs R7.

Is this clearer?

Re: high voltage BJTs
Most manufacturers no longer make high voltage BJTs. The IGBT has replaced the BJT for most power applications.
Check industrial surplus sites for parts salvaged from motor drives and so on for high power (> 100W) transistor modules for very little $$.

Do be aware that BJTs and their derivatives (IGBT) often cannot be used at the upper end of their voltage range to pass much current. Second breakdown, a phenomenon where the electric field is sufficiently nonlinear to cause local overheating, restricts the safe operating area of most BJTs. The magnitude of the problem depends on the geometry and doping of the device and is usually specified in the data sheet. If there is no SOA chart for a transistor, assume that the SOA drops 2x as fast beyond Vce > 10V on a log log diagram.

FETs (mostly) are immune to second breakdown due to their different current geometry.


[Edited on 11-2-2006 by densest]

[Edited on 11-2-2006 by densest]

@ densest

That image is clearer but still leaves some
of the connection paths to the imagination .

I gave up on circuit maker software and
resorted to pencil and paper . I have seen
some very good circuit graphics on the web
and I wonder is there some CAD program
or dedicated software for circuits that can
be conveniently stolen for personal use

I haven't looked on the FTP yet , and maybe its already there . Some of these programs even run
very sophisticated color graphic animated sims
with highlight frames showing what is occuring
in certain branches , waveform graphics and all ....
like an inset frame for a virtual oscilloscope . I have
got to have me one of those , to keep from
working the virtual Tektronix screen running
inside my head

@ Twospoons

If it wouldn't be too much trouble , would you mind
running that simulation again with these specific values ?

I have made a legible schematic using an " E " CAD
software and assigned some values which should
work .

See attached file .

Thanks for the link . I'll probably build the device and test
it in half the time it would take me to learn the simulation
software . And I'd bet good money the sim will return an
erroneous evaluation on a novel circuit it's never seen before , since it can't give a canned answer , it feeds you bullshit by default when it doesn't really know .

Suppose I don't agree with the sim projections ?
The only things I ever burned up was from following
manufacturers schematics , before troubleshooting
the design and figuring out what they had backwards
that technicians discover later in troubleshooting and
then put the way it should be in the first place

Technicians really are the best engineers ......
maybe because they get the job later of fixing
what's broke or making work right what never
would have worked right before they got it on a bench .

Open the last file I posted and resize it larger if it doesn't fill the frame , or just click print . I thought I did a clean job
with the schematic " to share with the rest of you " ......
right there .

Quote:

Originally posted by Rosco Bodine Technicians really are the best engineers ......

Here's another circuit for you to consider - with simulation results

Its your same source-follower concept, but using one N-ch and one P-ch mosfet. Pretty simple, eh? It also works with BJTs, though you might want darlingtons for any sizeable current.

Note there is a small amount of distortion around the zero crossing - cause by the gate threshold voltage of the fets - but its a soft transition so shouldn't cause your motor any trouble.

Attachment: ACRegulator.pdf (14kB)
This file has been downloaded 898 times

Hey Tim , If that sim software is so good ,
then why didn't it flag that particular transistor ?

I caught it because I was curious about the
specs on the P channel device and looked it up .

Anyway it does simplfiy things considerably if
you can find complementary devices . I am scrounging
parts to build , and keeping it cheap

Seeing there are a lot of surplus high voltage N channel Mosfets available for cheap , I focused on them .
There are also some high voltage NPN transistors
available for cheap , but the beta really stinks for
the high voltage bipolars , so N channel Mosfets rule
in the performance versus cost scenario .

It depends on whether the breakdown characteristics are in the model for the fet. A sim is only as good as its models. The point is, it gets you in the ballpark really fast. I just picked those fets at random , because I couldn't be arsed looking up the specs.

A Dirt-Cheap, High Current Power Supply

Further revision of my earlier circuit idea has brought
this design process to a point where I think the device
is ready to build , after I do a final check of my calculations
to try to find any errors or see if any values may be adjusted
to any advantage in refining what I have now .

I have added the circuit which provides a full voltage
startup pulse , adjustable upwards to a defined
burst quantity of full voltage cycles , so that when the stirrer
is switched on at a minimal speed setting , the starting
torque is greatly increased to give a clean breakaway
of the rotor into rotation , in an adjustable way that
should prevent any overshooting of the set speed .

This power control circuit combined with the PSC motor setup
having a squirrel cage fan and eddy current loading on
the lower endshaft , as I have described earlier in the thread
will result in what I believe will be a magnetic stirrer
drive scheme having superior performance and durability ,
well beyond the performance of the top of the line products
which are supplied by the major manufacturers . And if this
belief proves to be true by the performance of the prototype
which I am building , then this is state of the art in the making
( and that wouldn't be a first at this forum either )

The original attachment here has been replaced with
a corrected schematic which deletes a capacitor filter across
the power switch , for reason that it could cause a problem .
See the posts below for more about this .

[Edited on 16-2-2006 by Rosco Bodine]

I'm just going to sit down, watch this thread and laugh when it lets out smoke.

Tim

There you go with the negative vibes ,
trying to jinx my brainchild with self-doubt

I'm scrounging parts together and I'll give an honest
accounting of how it works or doesn't work .....
the unvarnished truth , such as the case may be .

Honest , if it burns it will be my first smoker and
I've put together a few things over the years .

You younger folks were making fun of my arcwire crossings
on hand drawn schematics that went out of fashion
in the 1950's . I can't read the copyright dates in
the books I learned this stuff from because I forgot how
to read Roman numerals ! So you are probably right
in hinting I needed to catch up to the times . It took
me a good two hours to learn how to use the ECAD
software to draw " respectable " schematics .

So there now .....I'm a modern , even though I still
miss riding the DC3's and DC4's and Constellations
when they were in regular airline service ! I am a
pre " jet age " sliderule operator dragged kicking
and screaming into the age of the inkjet published
virtual drawing with a schematic tucked in my pocket
that I see no reason shouldn't work like I think it
will .

So if you see a glaring fault , please elaborate .

Do you think the trickle current through the 26.5K reactance
of the .01uF cap across the open switch will trickle charge the
RC timing circuit for the startup pulse , defeating it ?

If so the cap can be omitted , it was sort of a last minute idea
I really hadn't thought about very much .
I'll probably leave it off just to eliminate that potential gremlin . Probably it is better to put a varister across the motor to clamp any spike , and just leave the open switch open . Yeah , I think the varister makes more sense .....
so I'll change that detail .

Thanks for the suggestion Why didn't I think of that

Earlier in the thread TransZorb was mentioned by densest .
Across the motor leads is probably the way to go here if
there is an appropriate voltage rating TransZorb for the task , and I'll defintely lose the cap on the switch because its a potential problem .

Update:

The attached schematic in my last post above has been updated with a corrected schematic deleting the anti-arcing capacitor which I had thoughtlessly placed across the switch without thinking it through . A suitable value TranZorb is
recommended as an option for putting across the motor ,
but it may not be necessary . The power stage for this
device is hopefully rugged enough not to be vulnerable to
the transients associated with a small motor load . I tried
to make the vulnerable part of the Mosfets , the gates ,
as bulletproof as I could , knowing that the toggle switch
and full power setting or hot startup pulsing feature ,
would be used at times to jog the drive in on-off fashion ,
occasionally being used this way to shake a stirbar free which may be caught in a dense mass of crystals .

There are a few final changes which I am still making
in the circuit before I consider this a completed design .
So in no way consider the attached schematic above as being
a finished work . There are some revisions which
I will be posting with an updated schematic when the calculations are completed and the edits made for
the values of components I will use .

[Edited on 17-2-2006 by Rosco Bodine]

The attached schematic now shows the above mentioned
component revisions / additions . It is now closer to completion . In terms of arrangement of components
I believe the circuit is complete . However the values
for the components are not fully analyzed and checked .
So there may be some changes yet made , in the way of
further tuning and calibrating the system . I am mainly looking at optimizing the RC time constants for the startup pulse controller stage since that is the last section added .

For you fellows who were following the circuit evolution
take a look at the timing circuit which biases Q4 .
The idea here is that on initial powerup Q4 is off and
allows the entire divider string of the control pots to
float to the potential of the positive rail , applying full
voltage reference to the gate of Q3 and followed from there
to the Output Mosfets Q1 and Q2 . While this is occuring
the capacitor in the zener regulated 10V charging path
is rising from 0 Volts towards the 1 Volt or so needed
to cause Q4 to switch , which takes the end of the divider
string for the control pots to ground , and makes their
settings effective on specifying V ref . to Q3 . The time
required for the capacitor to charge to the switching voltage
of Q4 will determine how many cycles of full power will
be delivered to the load . The larger 2.2 uF capacitor which
charges much more quickly to the full voltage of the bridge ,
acts as a virtual battery , which supplies power continuously to the 10V regulated timing circuit between cycles , so that
once Q4 has switched on , it stays switched on through the zero cross and into the next cycle , and the timer controlling
Q4 does not reset , until power to the bridge itself is interrupted and both caps bleed down .

[Edited on 17-2-2006 by Rosco Bodine]

Quote:

Originally posted by 12AX7 I'm just going to sit down, watch this thread and laugh when it lets out smoke. Tim

Hey Tim ,

Screw the SPICE simulation for this simple circuit ! .....
The conceptual and mathematical analysis and a discerning schematic reading is sufficient to say " this will work , so build the damn thing " ........ and that's from the old school , " Old Spice " sliderule jockey , SPICE illiterate
as I am . If I'm wrong , then I'll have to eat my share of humble pie when you fellows nail my ass to the wall
here with well deserved ridicule ......later ,
* if * the prototype burns . ( But it won't ) I'm not
worried about a design after the point where I can visualize
the intended result as a mathematical certainty ,
the predictions are over and it's time for proof .

I'm a great believer in perf board , legwire bending ,
and soldered connection " simulations " which run the way
you " figured " when you plug the damn thing in and throw the switch !

I look at this dedicated circuit which I have designed for a niche application , and without any personal bias from ego
afflicting me with any modesty either .......
my most objective opinion would be that obviously it was a genius who designed this little work of art

And the design is damn good too , absolutely beautiful .
If she was a girl , she would be one tough bitch ,
a little top heavy maybe ....but hey I like a girl who
sports a substantial package and puts out a little heat

So for all you jokers heckling and naysaying ,
I keep looking at this thing and looking for the fault ,
trying to spot the defect and I honestly don't see a damn thing wrong with it . In my opinion it will work and it will
work as intended .....so if you see something there in
that last schematic , which just doesn't add up or looks
wrong .....hey speak up and point it out to me ,
because the simulation I have been running on this thing
in my head keeps saying it absolutely will work in the
way it was designed and intended .

I still say this thing is a work of art , a beastie from
Planet Analog as it may be .....analog is not bad ,
when analog suits the application perfectly well ,
why complicate things going digital , and lose the
stepless smoothness you have with " hydraulic logic " ?

Have you ever flown a turboprop with a constant rpm
variable pitch propellor ? Smooth as silk , and no
digital logic involved . Similar regulation concept there
as what I am about here ......there is feedback and
governing , regulation inherent in the system as
" hardware logic " so the power feed just has to
feed power , and the mechanicals automatically
do what they are supposed to do with that power
they are getting .

And for those diehards who would insist on
adding digital rpm sensing and closed loop " servo locked "
operation .....well think about the advantage
there is about a system which already has a
great deal of inherent regulation , and how much
smoother and responsive it will be to amplified feedback
since the error correction required will be so much smaller
than for a system which fully relies on active external
regulation to maintain a set speed .

It's like the situation of a cruise control on an automobile
with a 2 liter engine approaching a grade , versus the
cruise control on an automobile with a 5 liter engine
approaching the same grade , the cruise control on
the car with the larger engine is going to have less
math to do and less error to correct to maintain the
speed of the system under the changing load .
No matter how good the cruise control , when
you are a passenger riding through hilly terrain ,
the vehicle with the larger engine is going to by
its nature provide the smoother ride .

That certainty is at the heart of my purpose of
using a specially configured drive motor in a
10 inch square stirplate which is a several times
" larger " motor in terms of its actual performance
than those deficient motors typically selected by
the commercial manufacturers , while it actually
uses no more electrical power than the junk they
are using instead .

What I am doing here is like the difference between
a " mini " and a Cadillac autobahn edition in terms of
inherent " reserve power " , available torque , ect .

I'm way too old to " go back to school " if I didn't learn
what I needed to know , to know this circuit will work
when I was in school thirty plus years ago .....

So I'm just going to build this thing and throw the switch
and see what happens

I should be taking bets on this thing so I could pick up
the extra money ......because if I had to charge for this
circuit design instead of making it a freebie here for
all my nerdie online counterpart friends .....it would be costing somebody about 200K for the R&D work carried
through to successful prototype for proof of concept .

I need a gold laminated pocket protector for this one ,
and a ball cap with gold embroidery which reads ,
" Captain Nerd " , and a silkscreened tie-dyed polo
shirt , with a pocket of course , carrying the logo
" Nerds Rule " . Then I would be a completed work
with my thick glasses However , I do have tortoise shell
eyeglasses frames instead of the ebony black , since I am a
" sport model " nerd

Quote:

Originally posted by Rosco Bodine Quote: Originally posted by 12AX7 I'm just going to sit down, watch this thread and laugh when it lets out smoke. Screw the SPICE simulation for this simple circuit ! ...

About the dropping resistor for the neon , I never
saw a 120V rated panel indicator where they weren't
built in , with the dropping resistor already inside
the threaded housing . Sometimes I have used a meter on one at the rated 120 voltage to see what is the actual current draw for 120 , and learn what the bulb itself is dropping , to calculate the added resistance if I put the same indicator across a 240 line or other voltage .

You wouldn't be nitpicking there , no.....
and yes I wondered for about two seconds
if I shouldn't show the dropping resistor for the panel lamp .....but you know I figured anybody skilled enough to
read the schematic already knows about neons , just
like that would be a fair assumption about the person
who wrote the schematic too , who is usually the same
one who designed the device .

The truth is I don't need the simulation for a sim I can run
in my head and see fine . I can read my own schematic
like I can read a shopping list for the grocery store ,
or the radio shack ......as the case may be , and I don't see any problem in this one so far as component function
and arrangement , all the signal paths and everything
flies the way it should ....if there's anything off it will
be fixed by a different capacitor or resistor value ,
and the ones I have now may be just fine .

So you have been looking at it with the old mental signal tracer , just like I have been doing , but you are seeing a problem somewhere.... so where exactly do you see the snag ? I may be slow sometimes , but I'm not totally braindead so if you point me at the defect , I'll see it .
Where is it ?

About the SPICE , that was specifically regarding Twospoons virtual model earlier , and I suppose misdirected frustration ,
since at least you do tell me where you see a problem , even if it isn't a problem .....instead of saying just that my computer is smarter than your computer and my computer says it won't work ....just because it says so .....but giving no further details

[Edited on 19-2-2006 by Rosco Bodine]

On the 19th day of clicking keys and calculations ,

I think I just nailed it .

I was trying to get the job done using no chips
if possible , but every thing I looked at was
just inferior to using 555's for the timing ,
so now that problem is hopefully solved the simplest
way . Wish every time I run into needing a
non-inverted output I didn't have to scratch build
a timer using an op-amp , or use a dual 555 .
Anybody else like to see a 10 pin package evolution
version of the of the 555's , with dual outputs ,
inverting and non-inverting so you could use
which output you need .....or both ?


I believe I have this thing supplied in a way that
it will initialize and power up logic stable , in under
2 milliseconds , perhaps 3 at the most , with sufficent
reserve in the high voltage " virtual battery " capacitor
to maintain the 555's operation and the timing status
until steady state operation matures with the first complete
cycle . If I did my math right , no decimals out of place ,
it should work fine with the values I have assigned .

Anyway see if this revision looks better ,
because I do believe this one nails it .

There used to be a dual CMOS version of the 555 ,
maybe LM7556 .....IIRC , but I haven't seen any being dumped as cheap surplus , or I would have used those
and not have to dump so many watts in the transformerless
power supply in the drop from 170 Volts to 10 Volts for
the timers .

I tried to tie into that supply in a way that wouldn't make the ripple worse than it is bound to be , figuring the 555's are stable enough to ride the waves that get across the zener .
There's a lot of difference between 1/3 and 2/3 of the rails ,
so the huge hysteresis there should keep the logic state
latched , even with a crude and noisy supply like I have
improvised to keep from buying a 3 dollar transformer
But there's too much delay in the power up of a separate
DC supply , so I couldn't use that approach anyway . The
duration of the startup event is so short , and begins occurring at the instant power is applied , so unless the
mains to the motor were delayed until the logic stage was
powered up and the chips initialized , a conventional power
supply could not be used .

I looked at all the motor controller chips before beginning
this effort , since none of the motor chips have the capabilities of doing this from a purely hardware level .
You have to program an EEPROM to essentially be a BIOS
for your motor control system , and even then there's things
you can't do with the turn of a pot , that I can do here .

I have used 555's before in motor controls which are associated with refrigeration compressors , to sense
power interruptions as a " missing pulse detector " which
monitors the 60 Hz , and if the compressor is running when
any interruption occurs , the 555 assumes a compressor stall
before the event , and times the compressor out for two minutes , before allowing it to cycle again and see if the
current it is getting is within specs . So I don't see any
problem with using 555's in a motor control circuit , since
there already are numerous commercial devices which use the 555's in motor controls and they have no problems .

Edit above : LM7556 was the number for the dual CMOS
version of the 555 .

Anyway if it bothers you to think of a chip going into a
control system like this ......just try to think of a 555 as
a transistor with a few extra pins and a college education ,
a transistor array that will do what you wish a transistor
would do , but can't do that concert singing solo

[Edited on 20-2-2006 by Rosco Bodine]

OK, wants you are spinning it's apparently impossible to deviate you off course. The 556 is indeed the dual version of the 555 and can be purchased via CONRAD Electronics International Mail Service for 1.51 Euro.

Conrad Electronics International Home:
http://www1.int.conrad.com

Search:
Electronics/& Metering --> Components ---> Active Components ---> IC's ---> IC's - Linear ---> Timer IC's ---> ICM 7556 IPD

In Audio Amplifiers it's fairly common to use power up delay circuitry which only turns on the final stage after the whole System has charged up sufficiently, so nothing new here.

You can also use a Transformer with a primary of 110/220 volts input and a 110 Volts and 6-12 Volts secondary output. Now we are talking International, with only one flip of a "Shift Switch" on the back side of the Magnetic Stirrer (50/60 Hz included).

I have uploaded ~100MB of Books and Motor Control Circuitry Designs to Madhatter's FTP services.

I cant Sing, so you will have to go on a Solo Tour by yourself.

[Edited on 20-2-2006 by Lambda]

Yeah that's a nice feature in high power audio amps
having the filtered relays to eliminate speaker pops
that would appear during switching transients .
Of course it would be possible to get more elaborate
and go that route , but you couldn't hide the fraction of a second perceptible switching delay which would appear
at the toggle to the user , and the effect would be
" strange " to someone who doesn't know why they
have to stand there growing older by a hundred milliseconds
just bored and waiting for the stirrer to finally decide to
start turning A fast gun or a son of a gun could clear
a room full of trouble and be reloading in half that time

Quote:

You can also use a Transformer with a primary of 110/220 volts input and a 110 Volts and 6-12 Volts secondary output. Now we are talking International, with only one flip of a "Shift Switch" on the back side of the Magnetic Stirrer (50/60 Hz included).

Yeah thanks for those . I have enough reading there to keep me busy for years

Quote:

I cant Sing, so you will have to go on a Solo Tour by yourself.

On some of the " industrial control " applications I like to
keep control circuits purely hardware logic where possible
and stick with linear chips . Everybody remembers the
" millenium bug " worries and what programmables might
be affected ......so there's no point in making basic control
circuits more complex than they need to be , just make
'em smart enough to do the job .....and too dumb to argue
It's the chauvinism of satisfied chip masters everywhere ,
enjoying the waltz of the flowers with satisfaction that these
obedient little minions know their place


[Edited on 20-2-2006 by Rosco Bodine]

OH man, ... Rosco !, ... you are just too bad, ... just too bad man.

How do I deal with this spinning wheel without cutting myself on those fine threads.

So now, ... you want to go IC, ... how about going PIC ? (don't read "Dick").

Eric's PIC Page:
http://www.brouhaha.com/~eric/pic/

Articles:
http://www.rentron.com/Myke3.htm

I have many Motor Control designs using PIC's, so just call the shots, and I will Shoot. You can tell (Program) this monkey to do anything, and if the climb doesn't suit you, then just reprogram. You can preset a variety of programs, all to chose from, depending on what is desired. Maybe you want your Hotplate to rise in temperature at 8 Degrees per 7 Minutes up to 73 Degrees, and gradually want the Stirrer to decline in speed from 600 rpm to 300 rpm during this period etc.

Now, I hope you won't get grey hairs over this one, ... will you. You can also start off by taking a few of mine, that will give you a "Head Start".

Rosco !, ... you are just too bad, ... just too bad man.

LOL , I don't want an RS232 interface on my damn soldering iron

I want pure hardware logic all the way on this thing .

There was a news item today about a 62 year old
great grandmother having a baby .....

and I couldn't help thinking ,
" I wonder who's the lucky father ? " ....

I should be safe on that count , but there's always
the off chance of being the guilty party , you know
how these things go with paternity tests and all

Now, ... this is very nice of you, thank you for congratulating me on my new born baby.

My wife chuckled at the news and said later we
will probably hear that the woman was arrested
after it was learned the father was age sixteen ,
one of a procession of frequent visitors who
" came for milk and cookies " from the " nice old lady "

So how is it that a woman of her age becomes pregnant ,
well it must be like playing the piano , it just takes
practice .....practice ....practice , until you get there

The news did say she already had TWELVE children ,
so it would seem she has had plenty of practice

Anyway , not to get totally off-topic here ......there are
available TTL input points provided now with the circuit at its present evolution , the gate of Q4 being the most obvious
point where modulation from a feedback signal could be
applied to " servo-lock " a set speed which is tachometer
regulated . Any sort of programmed time and speed profile
which may be wished could be input to the gate of Q4 .
And there are other ways in which the circuit could be
accessorized with extended functions , but would not
be crippled with any of those options " NOT enabled " .
I wanted a circuit which would give good performance
inherently , good enough stand alone for just about anything , but also could be adapted to enhanced functions with later " add ons " , like servo-locked tachometer based speed control or timed period sequenced speed profiles .
I would make those functions switched options on a
separate controller stage , a separate functional " block "
from the power stage I have shown here . Those options
and their schematic would be on page 2 , not yet written ,
and connected to page 1 by 3 or 4 wires if you follow my
meaning .


[Edited on 21-2-2006 by Rosco Bodine]

There's a need for biasing a transistor which will
be used as a switch so that it has positive feedback
to the gate , so when it begins to switch it will make
a positive transition just like a relay , and hold that state
at a lower signal level than was required to transition in the first place , behaving a corresponding way when making the reverse transition . This can be done using discrete components , on one transistor but better by using a complementary pair to create a bistable sort of
flip flop which toggles abrubtly to on or off and latches
there until a new transition signal level signal forces
a change of state . This is such a common task that
to save labor and the cost of using discrete components that chips like operational amplifiers and " timers " have been developed optimized for the task . The label
of " timer " is actually a misnomer for the 555 type chip
since that timer function is only one of the applications
where it is defined in function by what external components are selected . I more usually use it as
a switching device having defined level transition
states at 1/3 and 2/3 of the supply rails , a signal
comparator which drives a flip flop controlled output .
It is a logic device arrangement of a very basic but useful form , a sort of rudimentary analog to digital converter . This takes all the uncertainty out of the switching of
a single transistor which can fail to switch properly
under slowly changing or noisy signal conditions .
No chance of that happening with a flip flop , it has a binary output only , logic 0 or logic 1 state ......
fully off or fully on , and nothing in between .

I do use a calculator . The first scientific calculator I owned
was in about 1974 and it was a Texas Instruments Scientific with 1/2" Blue LED readout . It took four penlight batteries
to operate it , and IIRC in todays dollars it would have cost
over a thousand dollars at the time . But I often do the
familiar calculations in my head because I know the answer
in shorter time than it would take to key in the problem and
hit the equal key

[Edited on 21-2-2006 by Rosco Bodine]

The next generation of modified computer power supplies

Tired of blowing computer power supplies? I sure am. So I built this device which plugs into any ATX computer power supply.

I only paid about 30$ total, for the case, the electrode clamps, a switch and a couple binding posts. Everything else came out of computers and other equipment which I dumpster dived at uni.

Upper switch turns the unit on, the lower changes the voltage between 5 and 12V.

It is not variable current which would be ideal, but I lack the ability to build a variable current supply.

[Edited on 12-11-2006 by The_Davster]

An ATX to Lab Power Supply converter box !

Great minds think alike

I have have been working on a very similar concept for
an affordable low voltage high current supply ....
only trying to make it variable voltage using some added
circuitry along with the mechanical switches .

One of the ways you can get a stepwise voltage reduction which will have some stability is to string
a series of schottky power rectifiers each on a
small to medium separate heatsink , and depending on the current you will get .3 to .7 volt drop across each
diode . Another method is just to string a coil of
heating element between ceramic insulators , and
use an alligator clip to latch onto the coil at different
distance points along the length to introduce more or less
resistance in the current path , and dump the voltage
drop as heat . If you use a Y with two alligator clips
and leave one of the clips connected as you make the
moved connections stepwise , before disconnecting
the first position clip , there will be no huge arcing from
breaking the circuit .

These are less elegant solutions than a solid state
voltage regulator adjusted by a control knob like
a volume control .......but whatever works , works ,
and every one of these uses the same electricity ,
whether it is fancy or simple .

Update :

@The_Davster

Having my fingers crossed and hoping I didn't overlook
any potential snare in the design concept ......

I think I have completed the conceptual design for
the 0-100% *adjustable output * solid state
" voltage regulator " , that can be powered from an ATX power supply , and which has been discussed at length
in whimsy in the " Damn I love whimsy " thread .

The adjustable version is * not * soooo complicated
once the design is figured out , after that it is just a matter of getting parts and soldering the wires . Don't
sell yourself short with that talk of not having the
ability , this is not an advanced level construction
difficulty ......even though of course it is an extremely
advanced design

Thanks to 12AX7 for challenging me to attempt the
design , and discussion of design considerations ,
and also to Twospoons . The schematic isn't drawn ,
but it is so very nearly identical to an existing circuit
that I may not even bother , but just scribble noted changes on the existing schematic in the application note
and work from there .

[Edited on 19-11-2006 by Rosco Bodine]