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0-30V Stabilized Power Supply


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Whether you use one, or multiple transistors, the total power of 114W must be cooled somehow.  Unless separate heatsinks are used for each transistor, then the problem still exists.  Remember, though, that it is 114W if the outputs are shorted together - that's pretty unusual, so the normal running mode should be a lot cooler anyway.

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  • 5 weeks later...

Why do you show an LT1038? it is obsolete and is not made anymore.

It is impossible for it to dissipate 32V x 10A= 320W. Its datasheet shows that with a huge heatsink with fan or with liquid nitrogen for cooling it can dissipate only 120W. Its control circuit gives 10A only when its input to output is a few volts and cuts the max current to 2.5A when the input to output is 30V.

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  • 4 months later...
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As a student I built this circuit in 1982 from a circuit diagram I found in an electronic magazine at the time.  Built it as a dual supply unit with analog panel meters, modified a small bit to incorporate different reference resistors to o offer current ranges to 100ma, 1A and 3A with an SCR added for current cut-out option.  Has been using up till now (more than 30 years) on my workbench.  Still think it's an excellent power supply.  I will now re-build and construct it more professionally.  So glad I found the circuit again and the upgrades on this forum.


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  • 3 weeks later...

Sine you need a maximum output of only 15V and since most ordinary opamps have a maximum supply voltage of 36V then use an 18V transformer and the -5.6V negative supply as in the original project. The BD139 driver transistor and two 2N3055 output transistors in the latest version of this project should be used and the value of the resistor in series with the voltage calibration trimmer must be increased to set the maximum output to +15V.  

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  • 8 months later...

hi guys, i have the original kit from greece , i made it in 1995 and some day it was burned.

i did the audioguru rev7 update with mc34072 and all the changes. only thing i didnt change is the 12000 cap , i am using 2x3300/63v cap and 28vac transformer.

VDC is 39volts , ref voltage is 11,8 , negative voltage ok .

i have checked all components twice.then the following happened:

when i increase the voltage , it goes from 0.0 to 30.0 SHARP, BUT at 6.7 volts there is a "jump" from my panel ANALOG voltmeter to 8,7 volts ! i checked with the oscilloscope and it appears that at 6,7 volts there is a huge noise that the analog voltmeter averages and thats the cause of the "jump".

if i use a load that requires less than 6,7 volts everything works fine , lets say 100 ohm load the psu works fine cause it uses less amps (30/100=300ma) and current regulation works fine.

if i switch to 10 ohms load (30/10=3A ) that can use the full spectrum of volts and amps ,the power supply goes INSANE , it RINGS SO LOUD , and it even BURNED the C7 cap alive with flames...

if i use a 2ohm load , the psu increases the voltage BUT after the 2.2 amp it rings again (till 2.2 amps current regulation works fine).

if i short the outputs the psu goes over 3amps no matter what i do with the volts or amps (exception if i use 30volts and i short the output , the current regulation works , under 30volts if i short the output the needle goes over 3 amps the the ringing happens (the needle bounces a lot too).

probing at U2 shows insane ringing above 3-4 volts but after 20v it smoothens somehow.R12,C6,C9,C5,C7 seems ok but still lots of ringing.. most ringing is at pin6 of U2 and at the base of BD139.


i have checked everything after the blow of C7 in order to see what might be wrong or burned and i really cant find anything misplaced,wrong value,cold joint etc.

does this behaviour ring to any of you any bells for the cause of the problem? i am going nuts with this psu...


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  • 5 months later...
  • 2 weeks later...
On 5/20/2018 at 5:14 AM, Dave Laurenson said:

Hi All,

I saw this post by Liquibyte, and decided to take up the challenge of offering suggestions.  First, I'd like to say that I've enjoyed looking through this thread, and am very impressed with the work that has been done here by Liquibyte, Audioguru and others.  I have made some alterations to this new design, BUT I've not yet constructed it.  However, there are a number of things that I discovered when simulating with LTspice.

In the attached, I've made a number of alterations - rather than using a diode to ensure that the voltage reference is pulled down only when U1 is active, I've used a transistor.  The reason is that if the output were short circuited, then the inverting input of U3 would be zero, so U3 can never get the inverting and non-inverting outputs equal.  Hence the current is only limited by the output transistor drive capabilities since the minimum of the non-inverting input is the diode voltage drop plus the minimum output of U1.  Instead, I've used a transistor which can pull the non-inverting input of U3 very close to 0V (VIN-), which will be less than VOUT-, so the output of U3 will drop, and cut the voltage at VOUT+.

The second major difference is to remove the unnecessary output transistor Q4.  A single 2N3055 can drive up to 15A, so doubling up is not necessary.  (In fact, unless the transistors are well matched, it may have no effect whatsoever as at these "low" currents one transistor would carry the bulk of current if the matching were not perfect).  I was puzzled by the need for R13 until I realised that this is supposed to be part of circuitry to limit the current output of Q3.  I'm assuming that at some point in the past, the diodes that make this work were dropped - perhaps to keep the voltage up under high drive conditions?  In the redesign I've added three diodes from VOUT+ to the base of Q2.  If U3 tries to drive too much current through Q3, then the excess drive current will be routed through the diode chain, effectively limiting the drive current into Q3.  If the voltage is dipping under heavy load currents (less than the limit of 3A), then the output resistor can be reduced in size.  However, the consequence is that the maximum output current spike will be higher.

One other final structural modification is to separate the voltage sense and current sense parts of the circuit to allow the common Voltage/Ammeter module to be installed.  As I've not built the circuit yet, I don't know what the internal resistance of the ammeter is, so I've put a nominal 0.15Ohm resistor in there.  Obviously this should be changed to whatever is appropriate.

With a little reorganisation in the drawing, which includes some test circuits: a 555 astable which has power spikes as it is not decoupled, a resistor that is suddenly shorted out at 0.5s, and a resistor that varies between an almost infinite resistance to zero in a way that should make the current rise linearly up to 0.5s, and then the voltage drop linearly.  Also, I've included a period after 1s when the supply is switched off.  When I did this, I found it necessary to modify the power supply to U1 to ensure that it continued to limit current, otherwise I ended up with a large current spike after the power source had been removed.  I've also added a few notes discussing things I've discovered when changing things around.  I'm offering this revised (but note UNTESTED) design to the forum.

Just one note, I've seen pictures of some builds, and am slightly concerned that the casing of 2N3055 is not covered by everyone.  The case of the 2N3055 is the collector, which will be at around 38V.  If someone connects VOUT- to earth, then the full 38V will be present on the case, with whatever current the transformer can supply.  Under the right (i.e. wrong!) conditions, this could be fatal.  Please make sure the case is covered!

If anyone builds this, then I'd be really interested to hear how they get on.  If you do, please try to understand how the design works first - working with high currents with an untested circuit is not something that should be taken on by those not very familiar with circuit design/construction.  My plan is to build a lower current/voltage version of the supply (I really don't need 30V, nor 3A), but finding the time to do this is my biggest problem...



Dave,   Can you provide a sketch showing  the transistor layout between U1 and U3, as well as your modified the power supply to U1?

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  • 5 months later...

its this schem,except im using a 5.1v zenner for the -v supply not the regulator+ im using the mc34071 opamps.,in supposed cc mode the led lights but i can still increase the voltage and the output waveform is horrid,full of spikes,they increase in amplitude as i rotate the voltage pot cw ie increase the voltage,its fine in cv mode.


also i dont have the opamp etc on the top portion of the schematic

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If the spikes are only there while rotating the potentiometer then it is a bad pot.

If they are there in cc mode always then you can trace them back through the op amps output to inputs until you narrow down the source.

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  • 5 weeks later...

Hi, I have a problem with output voltage. when it's measured without the load I can only adjust it from 0.7V - 2V. However with 820 ohm load it can only output 0.8V - 1.2V. I can't find any high resistance "roads" (don't know how to call them) on the pcb. Any ideas what can be wrong with it? The schematic is a bit adjusted from: https://www.electronics-lab.com/project/0-30-vdc-stabilized-power-supply-with-current-control-0-002-3-a/.

I attached eagle .brd file and screenshots from the same file. Also I use 100k and 10k pots. to tune and fine tune the voltage and current  (can this be the problem?)

The transistors are 2n3055, two together with 0.1 ohm resistors at each emitter. 

Thank you for any advice. 




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The best you can do is to start at the  output transistors and work your way back through the circuit. It is impossible to diagnose homemade circuits at a distance as there are just to many places to go wrong.

For others never build something you can buy cheaper. Get two at 8$ each - one for parts.




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