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0-30 Vdc Stabilized Power Supply


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Hi Divljo,
I think your current regulator and Q1 should work with the 7805 and 7905 regulators and R23 and R24 removed. The fairly high DVM display current is overloading the negative 5.6V supply.
You can power the DVM regulators with a separate transformer, rectifiers and filters.

The current adjustment comparator, U3 needs the 5.6V negative supply. ;D

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hi audioguru...
my projects transformer is 150VA...my C1 is 10000mikroF 50V mounted on pcb...
my rectifier is MB356 35A 600V fast recovery...
i checked every connection on pcb...all is ok...i could not mistaken the conection of elements anywhere beacause i use the orginal pcb design,did not modify it...i used the parts list posted by you in this forum...

so the problem is that i cant get the proper amperage on output...
i think that some values in current limiting section are false by design...the amp pot is on maximum yet it limits the curent to 2.2 amps...with whatever the voltage required for the load...

my question:what can i modify to get more amp control on output???
please help...
has anyone succeded to build this suplly and got 3A on output???

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well, you are wrong - LED is still working even without reg circutry

And current pot isn't working! Is it possible that U3 is damaged?

Neverthless, I ordered from TI free 5 samples of OPA445 :)

I haven't tried putting Q1 back but i think it wont work because in the first place, reg circutry wasn't connected when Q1 was in his place and circuit didn't work...

I must say that drop on D7 is 0.1V..that should be 5.6V, right?
And other Zener, D8 has drop of 5.1V...even that is confusing (at least to me ;D )

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Hi Divljo,
There, you see? Your -5.6V supply doesn't work and therefore the U3 current regulator comparator doesn't work either because it needs the -5.6V supply. Check its 7 parts and replace U2 or U3 if they are hot.

Your voltage across the 5.6V zener diode D8 is low because you probably used a 1W zener diode which is spec'd with a current through it of 40mA. In the original circuit, the high 4.7k value of R4 produces only about 1.1mA through D8. My mod is to replace R4 with a 1k resistor and replace D8 with a BZX79C5V6 low-current zener diode that is spec'd at 5mA.
Then the project's voltage and current regulation will be superb! ;D ;D

Hi Costa,
I calculated the voltages, currents and resistors for the project's current regulator and they are fine:
1) 3A through the 0.47 ohms R7 = 1.41V.
2) The voltage at pin 6 of U1 is supposed to be 11.2V if you use the R4 value and D8 zener above. Adding the 11.2V with the 1.41V gives 12.61V.
3) The total resistance of the current adjustment divider is 56k + 10k + 33 ohms = 66,033 ohms. Therefore the current in the divider = 191uA.
4) 191uA times the 10,033 added values of the two lower resistors in the divider = 1.92V.
5) U3 is a FET-input opamp so its inputs don't draw much current from the divider nor make a voltage drop across R21. Therefore with respect to the negative end of C1, with the current pot at max, the positive input of U3 is +1.92V and its negative input is +1.41V.
6) With the positive input of U3 at a more positive voltage than its negative input, the output of U3 is high and it doesn't limit the voltage regulator's input through D9.

With the current setting pot at max, this project should try to give more than 3A output.
Check the -5.6V of the negative supply and fix or replace its 7 parts, or replace U3. ;D


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I replaced D7 and there is same thing! Nothing happened! I changed positions of U2 and U3 to see if one of them is burned but everything stayed the same! I checked voltages at U3 and they are all 0V except pin 6 (35V) and pin 7 (35.6V)

What is the next element that I should look?

Later I will put back Q1 but I don't think circuit will work then...

And I removed R23&24 and regs from PCB...I'll put them on other trafo

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Hi Divljo,
Don't install Q1 without fixing your negative supply. The function of Q1 is to short the output of U2 to ground when the negative supply disappears when you turn-off the supply. You've been there and done that, with the power turned-on.
Your LED DVM circuit must have strained and damaged this project's negative supply.

People have reported that R2 gets hot and should be 2W. Maybe yours is burned out.
They also say that C2 gets warm. Maybe yours is open.
Then you should check the rectifiers D5 and D6, and the current-limiting resistor R3.
Maybe your C3 has shorted.

Maybe your rectifier bridge has an open D4 rectifier that doesn't pass the negative transformer pulses.

You have only a few parts left to check and replace and your project is nearly finished! ;D

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Thomas: Wher do you see that pin 2 is connected to the input of 79xx? pin2 of both regs are connected to gnd!

Well... my datasheet (SGS-Thomson) says something different:
When the reg is lying before you with its legs towards you and the writing on top, it goes from left to right: GND, Input, Output.
A 78xx, on the other hand, has Input, GND, Output.

Annother chip manufactory says the same:

But anyway, powering the dvms from different sources is a much better idea. Remember to use separate sec. windings for each dvm, because they will burn if a AM and a VM is connected to the same source.
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well, I've got some bad news :)

I left supply 15mins with 15V and 2.85A and measured voltage drops for op amps and some components...

pin 4 of U3 gets -0.02V :)
R7 1.1V
D6 2.4V
D7 -1.1V

and then something happened; Q2 started to smoke and I quickly turned off supply...it seems it is ok; checked E and C voltages; i turned on supply and with load nothing happens (maybe it needs time to screw up?)
Q2 is cold as ice all the time but when he started to smoke he was very hot :)

Also, R2 and R3 are hot! Both they need to be minimally 1W but I'll buy 2W
C2 is getting only warm, but is there any way to cool him down completly? Higher voltage?

And now the list of non-working components :)

C3 has 215Ohm resistance; -dead
D7 isn't anymore diode; it lets current flow through both ways  -dead
And now something weird...D11 is dead! Maybe it happened when Q2 started to smoke ;D

Rest seems to be OK

But, I'm going day after tommorrow to buy again all diodes, op amps and some resistors and some other things..and I'm gonna make new PCB, hope it is the last pcb for this project :)

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if anything can go wrong it will go wrong...murphy's law... >:( >:( >:(
my project worked fine all the time... :D :D :D
it was not faulty in any way...current regulator works fine....it delivers over 4Amps on 30Volts...
my mistake was that i used chinese,piece of shit,analog ampermeter (that i planed to use fixed on my power suplly) that was inaccurate, to say at least...
this ampmeter displayed 2.2 amps when there was 4amps for real...
i feel like an idiot...wasted so much time on trying to solve a problem that wasnt there...
sorry to you all that i bothered, especialy you audioguru...i know i've been a bit of a drag...  :-[ :-[ :-[
p.s. does anybody have a shematic of a led display digital ampermeter with range 0-5 amps and 0.1 accuracy...thanx...

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Guest GOO67

Hello!!  I have an old laptop that needs a power supply to test if it works.  It's power rating says:  15 volts 2.7 amps 40 watts, and I would like to know if this power supply will run this laptop.  Thank you for all replies.

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Hi everybody.

I have made This project nearly a years ago. and it is working everyday. but today I saw sth which is strange to me.

WHAT is the roll of    "R17"    ? (UP-Right, emitter Of 2N2219)
Is it there for more stability. I have seen same resistors in ICs Spec too.

ThanX in advance

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Hi Shariar,
R16 turns off the output transistor, and does it quickly.
Without it, the project's output voltage would probably rise if it is powering a low-current load, because of the leakage current in Q2 and Q4. The leakage current is fairly high because the transistors operate hot in this project.
R16 speeds-up the turn off because it discharges the capacitance of Q4 quickly. ;D

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Guest ElectroFreak

Hi everybody!

After a lot of time, here I am again...

So, i have built this power supply, and today i finnaly find some time to test it.
And, of course, something has gone wrong...  :(
Whell, when I turn it on, everything looked OK. All elements were cold.
Voltage regulation worked perfectly, from 0-35 V.
But ... when i connected a 12 V bulb and try to measure & regulate the current, suddenly - a smoke. First I thought that it was U2, but i defined that was R15!
I tried to define if R15 is only element that was dead, and then i found one more strange thing: D11 died too... ??? Everything other seems to be OK.

So, now i have clean 30 V output...  :(

But, one positive thing: i accidently short circuited output, and i saw that current limmiter works.

If anyone knows what the hell is going on, please help...

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Hi Elecrofreak,
If you used the original value of 1k for R15, it would smoke with about 16V across it. Maybe the pins of Q2 are incorrect, or maybe Q2's collector isn't connected.

About the only thing that would kill D11 is if it was shorted or connected backwards, and the current was set high. ;D

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Guest ElectroFreak

Thanks, Audioguru... :)

I used the 100 Ohm resistor for R15...
Q2's pins seems to be OK.
But I still can't figure it out how D11 burned.
So, I'm going to change R15 & D11...
Maybe it will work...  ;D

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I used TL081 ... OP445 not availabile in my area...
But something is strange here ... to me ...
I dont know....

Hi Electrofreak,
Your positive unregulated voltage is probably about 41V (across C1) and your negative supply is about 5.2V (across D7). It is strange that the TL081 opamp survives with the resulting total voltage of more than 46V across it since its absolute max rating is only 36V! :o

I don't know what happens to an opamp with way too much supply voltage since I haven't tried it. I would feel foolish to ask the manufacturer. ::)

What did you use for Q2? Maybe it breaksdown from overvoltage too. 
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