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0-30V Stabilized Power Supply


redwire
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.....work out some sort of voltage drop later on.

The high supply voltage problem has already been worked out for opamp U3 because it uses a -1.3V negative supply. So its positive supply pin is powered through a 10V zener diode which reduces its supply voltage by 10V.
Power your U1 and U2 from this zener diode too to reduce their supply voltage. Check the zener diode for heat.
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Guest liquibyte


The high supply voltage problem has already been worked out for opamp U3 because it uses a -1.3V negative supply. So its positive supply pin is powered through a 10V zener diode which reduces its supply voltage by 10V.
Power your U1 and U2 from this zener diode too to reduce their supply voltage. Check the zener diode for heat.


Like this?

Edit: removed pic to avoid confusion with other schematics.
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Another solution of this problem is to wire a couple of power diodes in series after the rectifier and smoothing capacitors. Each diode will reduce voltage with ≈0.7VDC.


I started asking about hooking up the TO-3's over at EEVBlog because it's a much more active site and I was looking for an immediate answer to my question.  I am getting a bit of negative feedback regarding the fact that someone thinks that this design isn't sustainable due to the fact that with a 28V transformer after rectification and smoothing that the voltage into the opamps is going to be around 50V.  Has anyone that's built the 3 amp version run into issues with this?  If so, what sort of solution did you use to fix the issue to get the voltage to less than 44V so as to not overload the max limits on the TLE2141's?.

Edit:  Nevermind.  I hooked up the filter cap and measured 45.1 VDC.  It's a little over the 44V max of the op amps which worries me a bit.  So I guess a new question would be, is there a recommended way to drop that to the 44V?  Voltage divider to ground?
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Guest liquibyte

Another solution of this problem is to wire a couple of power diodes in series after the rectifier and smoothing capacitors. Each diode will reduce voltage with ≈0.7VDC.


I had thought of doing that with some ER502's I have.  I'd like to keep the original circuit if possible and had thought that might be a viable workaround to get just under the 44V.  As it stands now, I get right around 44.6V so it might be a good solution.  Audioguru's suggestion to run through the zener sounds like a good fit too if the thing doesn't get too hot.  I'm assuming that if it does, I might be able to find a component with a higher wattage rating that could handle things.  I was looking at the 1N5925BRLG which is rated at 3 watts but I'm not sure what else to look for in a zener besides voltage and wattage rating.
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Using a TLE2141 opamp for U2, a negative supply is not needed. The inputs will work slightly below ground but go down to only 0V and the output will go almost to ground but goes only as low as about +1.1V in this circuit.


You are correct.  I  must have been thinking of another circuit.
   
On another note, there is no reason for U1 to need a 41V input rail.  It only needs about 13-14V in order to supply a constant 12.2 V.  Why didn't we connect the positive rail of U1  to the 10V zener like U3 and drop 10V?
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On another note, there is no reason for U1 to need a 41V input rail.   It only needs about 13-14V in order to supply a constant 12.2 V.  Why didn't we connect the positive rail of U1  to the 10V zener like U3 and drop 10V?

Like opamp U2, U1 also does not have a negative supply. With a good 28V transformer, with no load its supply is +40.5V which is less than its 44V maximum.

U1 can be powered from the 10V zener diode together with U3 if you want and if the zener diode is rated at 1W then it will get only fairly warm.

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Guest liquibyte


Like opamp U2, U1 also does not have a negative supply. With a good 28V transformer, with no load its supply is +40.5V which is less than its 44V maximum.

U1 can be powered from the 10V zener diode together with U3 if you want and if the zener diode is rated at 1W then it will get only fairly warm.


If I were to drop in two seperate 12V 1W zeners for U1 and U2 instead of all three going through the 10V would that be ok?  I have two sitting here that could be used for this if it's possible without disrupting the circuit too much.
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Guest liquibyte

So U1 and U3 through the 10V zener.  Maybe a voltage drop with diodes through U2?  I've tried to get a good drop after the rectifier but even with two power diodes I can only get it down to 44.3 volts.  I think the 0.7 volt drop talked about a lot is theoretical and not practical, either that or I have some really efficient diodes.

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Guest liquibyte

I've got it planned out now to run U1 and U3 through the 10V zener and I'm going to drop a volt point something through a couple of 1N4005's in series which should get me under my 44V max on U2.  I've been consistently running tests for the voltage after the smoothing caps and I get between 44.7 and 45 volts so I think this may work.

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liquidbyte ,  I  I personally think you are splitting hairs on getting to exactly 44V or less  on U2, but if it helps you sleep better, you could  put a 5.6V zener between the positive rail and pin 7 of U2.  Since you need at least one 5.6V zener for the project, it is likely you have a spare.  Hey, if thing don't work out just put a piece of wire across the Zener. 

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Guest liquibyte

I guess I am kind of splitting hairs but I figure it can't hurt.  I already soldered the diodes in so we'll see how it goes.  I appreciate everyone's help though, it is much appreciated.  Actually, the fun part really comes next when I try and design my own displays for this.

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Guest liquibyte

I wish I were that smart.  Just simple 4 digit volt and 3 digit current meters using led displays with max7219's or as1100's and atmega328p's.  I'll just be doing lego block designing, no need to re-invent the wheel.  I'd like to do more advanced stuff but I'm still just learning the basics.

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Guest rencajs

Hi guys! I just builded original power supply project based on tl081 opamps and now i realised that there was some major problems vith original project but now i cant find solution :(
The problem is that U2 is heating up but in output there is only 200mV. I checked components and nominals and everything ir wright but still i cant find promlem :(
Could you please give me some advise?

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The original project used a 24VAC transformer that was overloaded at maximum power. It produced about 25.5VAC with no load then its peak voltage was 36V that was reduced to 34.7V by the bridge rectifier.
The opamps used this as their positive supply but U2 also has a -5.6V negative supply so its total supply was 40.3VDC. Its maximum allowed supply is only 36V so it fails. the 24VAC transformer does not allow this project to make 30VDC at 3A anyway because its voltage is too low (its power rating is also too low).

Many more parts in the original project are overloaded especially the single output transistor and its driver transistor.

You can replace the TL081 opamp with a TLE2141 opamp that has a maximum allowed total supply of 44V but maybe the overloaded output transistor or driver transistor have also failed.

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Guest liquibyte

Is there a specific procedure that you use to calibrate this circuit?  I've finally got both of my circuits working but am not sure where to set RV1, 2, and 3 when I start this up.  I know that setting RV2 and RV3 sets the limits of voltage and current.  What am I setting with RV1, what do I look for and where am I measuring from to get this set right?  I don't want to release the magic smoke by doing things wrong so I figured I'd ask how others have started.

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What am I setting with RV1, what do I look for and where am I measuring from to get this set right?

Set the voltage pot to zero and adjust RV1 so that the output voltage is exactly 0V. You will be able to adjust it from about +50mV to -50mV. If the output capacitor C7 is an electrolytic type then it will have dielectric absorption which will cause the output voltage to be a little positive instead of 0V. A film type of capacitor will not do this.
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Guest liquibyte

I'm actually pulling -100+mV at zero and no matter what I adjust, the voltage doesn't change that much.  In addition, the most I can get out of each circuit is around 10V, not the 30 I was hoping for.

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I'm actually pulling -100+mV at zero

I do not know what "pulling" is. If RV1 can adjust the output +/-100mV then that is good. Simply adjust for 0V.

no matter what I adjust, the voltage doesn't change that much.  In addition, the most I can get out of each circuit is around 10V, not the 30 I was hoping for.

Then you have something very wrong. I will look back to see what modifications you have.
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