0-30 Vdc Stabilized Power Supply

[audioguru2]

Hi Smokey,
Welcome to our forum. ;D
This thread discusses modifications to the original project to make it work properly.
I posted a revised parts list in this thread that has a TIP31A real power transistor replacing the little 2N2219, a 30V transformer and two 2N3055 output transistors etc.

In this thread we also discussed that the supply voltage for the opamps is about 49V which far exceeds the absolute max voltage rating of 36V for ordinary opamps like the TL071 or TL081. There are a few opamps with a 44V rating but I recommend using OPA445AP opamps that have a 90V rating.

Many members have made their own pcb and maybe somebody will sell you one. ;D

 

[smokyLED]

ok, who's gonna sell me a pcb with the update design?  ;D

 

[audioguru2]

The pcb is about the same as the original. Some resistors are larger but must be stood-up from the pcb to avoid charring anyway. The driver transistor Q2 has a different pinout than the original 2N2219 but needs to be mounted on the chassis as its heatsink. A big rectifier bridge replaces the original rectifiers but it also needs to be mounted on the chassis. The original pcb will be fine. ;D

 

[SupeR-NovA]

Hi to you all
first i would like to say that i'm new here, and this site & forum are great!

I would also like to build this PSU, but i want to make it DUAL.
in order to reduce cost/dimentions i would like to know if i can share the whole
area within the red line...
if not, please tell me which compenents I can't share
thanks!

P.S. if there any more sharable components outside the red line please do tell me

View attachment 37785

 

[audioguru2]

Hi SupeR-NovA,
Welcome to our forum. ;D
Why dual?
You won't be able to have one as a negative supply.
You won't be able to put them in series.

If they have their own transformers and your parts marked in red and are completely separate, then you can do anything with them except not parallel them.

 

[SupeR-NovA]

well... I guess you are right...
my problem is that I have nowhere to buy another transformer...
the one I have right now (center tapped 24v 4.1A) was found on a sidewalk

I guess I'll just build one and wait till another transformer rolls into my hands

 

[audioguru2]

1) replace Q2 with TIP31A (by the way, can i use B or C instead? i can't find the A type)

B and C are fine. They are rated for higher voltages.

2) add a fan and supply it from a 12v Zener and a resistor OR add another 2N3055, which solution is better?

The current gain of power transistors drops at higher currents and some are weak anyway. Your 4.1A transformer can power this project to produce 3A output if you use two 2N3055 transistors with emitter resistors and a pretty big heatsink. You can reduce the size of the heatsink if you use a fan.

3) replace the 4 1N5402 with a 4A+ bridge rectifier (is it really needed to connect this one to a heatsink?)

With 3A going through it, a bridge rectifier module gets pretty hot without being bolted to the side of a metal box, with some thermal grease.

I really don't care much if this unit won't supply exactly 30v or 3A.
my requierments are 0-24v 2mA-2.5A. will the current circuit plus the changes i described be enough for this?

It will have more output voltage at 3A if R15 is changed to 100 ohms.
It will regulate the voltage better using a BZX79C5V6 zener diode for D8 and 1k for R4.
C1 should be pretty big, about 12,000uF.
R7 should be about 10W.
R2 and R3 should be 2W.
The opamps should have a higher voltage rating than ordinary ones but not as high as the opamps needed with a 30V transformer. With your 24V transformer then MC34071 opamps are fine.

this topic got me really confused....

Yeah, I wish its designer got it right in the beginning.

 

[SupeR-NovA]

thank you very much audioguru... you cleaned up all the mess with your last post

 

[audioguru2]

Q: does the PCB on the site fits the version you just described?
for example:
1)does the MC34071 have the same pinouts as TL081 so that i can just use these instead?

Exactly the same.

2)do any components need to be stood-up?

R2, R3 and R7 will probably need their wires bent around under them. C1 can be mounted on the chassis with a clamp.

I also have two 10000uF/16v caps, can i connect them in parallel to get 10000uF/32v and will it be enough?

No, No! Two 10,000uF/16V caps in parallel equals a 20,000uF/16V cap. If you put them in series their value is halved to only 5000uF and the one with the lowest value will have more than half the voltage. Also their effective resistance is doubled. Buy a proper capacitor.

I used another cap for testing and the transformers secondary winding voltage doesn't exceed 30v.

The transformer's voltage will rise maybe 1.5VAC with a low-current load. The root of 2 times 24V = 34V peak. The rectifier bridge will have a voltage drop of 1.3V at low load current resulting in a DC voltage of between 32.7V and 34.8V. Add as much as you want for transformer tolerance and mains voltage fluctuations. Use a 50V cap. ;D

 

[kankundachi]

Hello dear all:

    Today I have finished the power supply circuit. But now I have a problem that's when the circuit is power on and adjust limit current. The limit current adjust range
only 670mA ~ 3.92A. The limit current should be 2mA ~ 3A but my circuit is not. When I found the current range is 670mA ~ 3.92A,U2 output (pin 6) voltage range is about 1.5V ~ 4.*V. Is the voltage range correct? If anyone ever has this problem,please tell me that's why. Or you have any suggesion tell me please,too. Thank you very very much.

Best Regards,

            Stanley

 

[kankundachi]

Sorry ! I forgot to say my circuit adjust voltage is no problem. Only adjust current has problem. Thanks.

 

[audioguru2]

Hi Stanley,
It sounds like the negative 5.6V supply at D7 isn't working.
U3 is the current comparator and its output needs to be able to go to a negative voltage in order for D9 to pull the output voltage down when the current through R7 exceeds the current setting.

 

[pigster]

Hi everyone,
i have just finished this supply, i have used all modifications mentioned in this forum except change of opamps. Btw, doubled 2N3055 is REALLY good idea.
All is working fine, i have only one problem and don't know if it is problem in construction or in design. If i turn the PSU on, there is huge voltage peek. For a moment the transformer output voltage appears on output (my is 28V). If i turn the PSU off, than i have about 35V on output and is falling down (as C1 discharges). When the PSU is turned on, it operates normally. Oh and R2 gets sometimes little bit hot (maybe someone can explain me why the combintion of R2 C2 is here, and connected directly to transformer output)

Thanks fo replies
(sorry for my English)

 

[audioguru2]

If i turn the PSU on, there is huge voltage peek. For a moment the transformer output voltage appears on output (my is 28V).

Hi Pigster,
Welcome to our forum. ;D
It sounds like the negative 5.6V supply comes up to its voltage too slow. Maybe R2 is burnt and has increased from 82 ohms. More info about R2 below. The negative supply connects to U2 which controls the output voltage.

If i turn the PSU off, than i have about 35V on output and is falling down (as C1 discharges).

Q1 is supposed to conduct when the project is turned off and then it will immediately drop the output voltage to zero. The negative supply has low-value capacitors that discharge much quicker than C1, therefore Q1 becomes biased on.

When the PSU is turned on, it operates normally.

Great! ;D

R2 gets sometimes little bit hot

Other people said the same thing so I changed its rating to 2W.

maybe someone can explain me why the combintion of R2 C2 is here, and connected directly to transformer output

The negative supply is a standard half-wave charge pump circuit. C2 charges through R2 and D5 when the transformer terminal is positive, then discharges through R3 and D6 into the zener and opamp negative supply pins when the transformer terminal is close to ground.View attachment 37795

 

[kankundachi]

Hi Stanley,
It sounds like the negative 5.6V supply at D7 isn't working.
U3 is the current comparator and its output needs to be able to go to a negative voltage in order for D9 to pull the output voltage down when the current through R7 exceeds the current setting.

Dear audioguru :

    If D7 isn't working,the vary with voltage (0~30V) will be exceptional. Isn't it? But I still
follow your suggesion to check D7 voltage on my board. The result is -5.50V. Besides I found Q2 bias-emitter voltage is 0.61V,Q4 bias-emitter voltage is 0.63V,R15 voltage is
0.06V(exceptional voltage) when output short. How about your opinion?

Best Regards,

                Stanley

 

[audioguru2]

Hi Stanley,
Your negative supply is fine. ;D
Maybe your R17, R18 or P2 has the wrong value.
Maybe your opamp U3 is damaged.

Look at my sketch of the current regulator U3 section without any load current, and think about P2 turned down:
1) The opamp's inverting input pin 2 is 0V.
2) The opamp's non-inverting input pin 3 is only +5.6mV.
Therefore the opamp's output is high and it doesnt do anything until the load current is about 12mA (12mA x 0.47 = 5.6mV) and the circuit will keep the load current at 12mA even if you short the output.

Now turn-up P2 a little, increasing the voltage at the opamp's non-inverting input pin 3, then the load current must be increased for the voltage across R7 and at the opamp's inverting input pin 2 to exceed the voltage on pin 3, for it to regulate the load current at this new current.

It is a little more complicated because the output 0V goes positive with respect to the rectifier's and filter's ground with higher load current and the 11.2V reference also goes higher by the same amount, increasing the voltage across the voltage divider with the P2 control.
Understand? ;D

View attachment 37797

 

[pigster]

Thanks for explaining negative circuit,
about the peek problem, i have checked all components in negative part, all is ok including 82 ohms R2. I have also done little experiment, i have connected LED to output of PSU, set voltage to about 1,8V, all is fine, LED is ligting, then i have switched off the mains switch and .... amusing efect happened as LED burned out.
Any ideas?

 

[audioguru2]

I said it before.
Quote: "Q1 is supposed to conduct when the project is turned off and then it will immediately drop the output voltage to zero. The negative supply has low-value capacitors that discharge much quicker than C1, therefore Q1 becomes biased on."
Maybe your C1 is defective and its value is much too low.

Does the project still have a huge peak voltage when it is turned on?
C1 having a low value might cause it.

 

[Sasa G]

Hi everyone
I made this PSU but voltage regulation dont work fine.
I have 0-60 % of P1 regulation 0-32 V and 61-100% of P1 constantly 32V.
What is wrong ?

Sorry for bad english.
TNX
Sasa G

 

[audioguru2]

Hi Sasa,
Welcome to our forum. ;D
It sounds like your pot P1 is broken. Its slider's voltage should go smoothly from 0V to 11.2V then is amplified to 0V to 32V by the output amplifier.