Jump to content
Electronics-Lab.com Community

0-30 Vdc Stabilized Power Supply

Recommended Posts

With this hum, you mean just noise, or it has impact on quality of output?

When the output of a "regulated" power supply has hum (100Hz in Europe or 120Hz in North America) then it indicates that the output is saturated and is not regulating the voltage.
The voltage changes of the AC input (including noise) and the ripple of the filtered rectifier are simply passed to the output. The output voltage will also change with load current changes.
Link to post
Share on other sites
  • Replies 2k
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

The original circuit should work fine up to 15V at 1A if you replace the old opamps with the newer higher voltage ones. You probably should recalculate the resistors that set the maximum voltage and c

February 23 above on this page has the latest schematic of the revised 3A lab power supply.

So Finally which version of schematic is correct  / flawless  to  build the PSU ? 

Posted Images

So, I need at least 28V 120VA transformer? But output with 28V or 30V transformer has also hum at maximum output voltage, yes?

When a 28V AC or 30V AC 120VA transformer is used then the output at 30.0V and 3A will be regulated perfectly with no hum.

There is hum when the transformer voltage is too low which causes the output transistors, driver transistor and opamp U2 to be saturated.
Link to post
Share on other sites
  • 2 months later...

i had the original pcb from ages ago so i modified it (at least i tried) with audioguru's changes.
however i am having the following problems:

voltage regulation seems to work, but when the current goes over 1 amp, i have oscillation on the 3055s and c7 gets very hot
u1 gets a bit warm
the current limiter works in a weird way, i mean, it limits current up to the middle position of the potentiometer then it allows current again. the led has a constant dim light and when the current limit kicks in it lights fully

now, i should mention that i could not find tle2141 so i used ca3140, the closest i could find here
also, i tried a higher value for c7, it reduced the oscillation, but it's still there
i replaced the d13,d14 with the original 5.6v zener, before, the led burned up

i am suspecting i have done something wrong modifying the old pcb, or the ca3140 is not proper for this i might try this on a stripboard if i have the time..

any suggestions?..

Link to post
Share on other sites

ok...i will try to find a tle2141..

funny thing is that in every shop i asked about it they either never heard of it, or thought it was obsolete. especially with the crisis here in Greece it is very hard to find components in stock anymore, maybe online..
i'll get the 2141 somehow and will check again the circuit

Link to post
Share on other sites
  • 3 weeks later...

hello. i am new in forum. i checked yesterday almost all 118 pages and i have to admit that you are all amazing. Audioguru you are doing really good job. I already built today 3A version (will upload pictures after testing it). I found also picmaster's Schematic and i am interested to build 5A version also. Can u point me where to find picmaster posts and part list. is there any forum where can i read about 5A project?

thanks alot for answers

Link to post
Share on other sites

Hi Srecenvid,
The 5A version has only a few changes from the 3A version:
1) More powerful transformer, 28VAC/200VA or 30VAC/212VA.
2) Medium size heatsink for the 10A rectifier bridge module.
3) R7 changed to 0.27 ohms/10W.
4) Three output transistors on a huge heatsink with fan and a 0.33 ohm/2W emitter resistor for each output treansistor.

I didn't save the design by PicMaster. I think he changed the calibration trimpot positions and changed all the parts designation numbers which makes talking about it difficult (R7 is now his different number etc).

Link to post
Share on other sites


I can't adjust output voltage down to 0V. Instead i get aprox 30 mV. No big issue but it would be nice to fix if possible. Is this something that could be solved by changing trimpot or resistor at offset inputs or is it a leakage i have to live with?

Output goes down to 0 volt when current pot is in its "closed" position.


Link to post
Share on other sites

hey. i have a problem. i built now 5A power supply, it was working great, until i did not try today it with 48v power transformer. now i have constant 35v voltage, also cant adjust it. anyone have idea what can be wrong?

The MC34071 or TLE2141 opamps operate near their maximum allowed supply voltage (44V) with a transformer that is 30VAC. A 48V transmormer voltage is much too high so the opamps are probably blown up. The transistors also might be blown up. Resistors and capacitors too?

Why did you try the transformer that has a voltage much too high? Using a stick of dynamite would be quicker.
Link to post
Share on other sites

hey. yeah it was mistake XD actualy i thought its also 30V power transformer. anyway it was not much wrong, only one mc34071 was blown up and 10A trimpot+potentiometer. after changing this enverything work great :). i am doing now also ammeter/voltmeter lcd panel... do i post some pictures or project files? thanks for help.

u know maybe if someone tried to do 10A version? or does it need other power transformer (toroidal transformer)?

Link to post
Share on other sites

u know maybe if someone tried to do 10A version? or does it need other power transformer (toroidal transformer)?

If the output voltage is set low, the load is shorted or draws 10A and the current-setting pot is set to 10A then the output transistors (six of them) will dissipate a total of 390W. How will you cool them?

The driver transistor cannot drive six output transistors so it must be made stronger and opamp u2 will not be able to drive the driver transistor.
The 30VAC transformer must be 424VA which will be enormous, custom made and very expensive.
R7 must also be huge.
It will not be practical. 
Link to post
Share on other sites


Created by I will supply the power. I am curious if the components are written on the connection (link), okay, or which is necessary to change the other values


what transformer would be needed for good performance?
220/24V 100VA ali 120VA

Link to post
Share on other sites

The original project is an old piece of garbage with many errors. It does not produce 30VDC at 3A and is not reliable.
That is why I fixed it. We talk about the latest fixed version on this and on another thread here. Look through this or the other thread to find the latest parts list (Rev 3) and schematic Rev 2, Mar 11/09).

1) The original project used a 24VAC transformer so its max output was about only 25VDC at 3A (not 30V).
Even with a transformer with a voltage too low, the opamps it used have a supply voltage that was much too high for them.

2) The transformer, driver transistor, output transistor, rectifier diodes and many resistors are overloaded and will fail soon.

Therefore the original circuit does not work properly and is not reliable.

Link to post
Share on other sites

Thanks audioguru.

I have 500 and 1000VA transformer 24V in my small lab and i can try to do also 10A version.

About heat and transistors i have really big cooler with water cooling, so that wont be problem probably, now i have only found enough big resistor for this...will check tomorrow my inventory and see what i have.

about driver transistor i was thinking maybe i can try and use 2 drive transistors and opams, but that will change scheme alot? or is that stupid thinking? or you maybe help me find enough big opamp and driver transistor... anyway good night, i am ready for experiment :), will check all needed parts tomorrow and see if it is even possible :)

Link to post
Share on other sites

I have 500 and 1000VA transformer 24V in my small lab and i can try to do also 10A version.

A 24VAC transformer voltage is too low.

About heat and transistors i have really big cooler with water cooling, so that wont be problem

I guess some people have liquid nitrogen.

about driver transistor i was thinking maybe i can try and use 2 drive transistors and opams, but that will change scheme alot?
Link to post
Share on other sites
  • 2 weeks later...

Ok Im trying to fix my project using the following info.

    Received the following email from Ivan on 02/2010:

    Ok. I bulid your project about a day ago. Mounted all the parts on the pcb and then concluded that there is some serious problems in this schematics. First, 2N3055 will overheat, so you have to connect two of them in parallel with emitter resistors 0.1ohm/5w. Second, maximal voltage between '+' and '-' of TL081 is 36VDC.If you connect them as it is shown in this circuit diagram that voltage will be about 45VDC, so they will burn down immediately. To fix this problem you have to reconnect all pins number 7 of U1, U2 and U3, emitter of Q3 and 'upper' end of R19 to out of an 7809 with 18V zener diode between 'common' pin and '-' of 3300uF cap, and input of 7809 connect to '+' of the same cap. Now, on pin number 7 and mentioned parts you'll have 27VDC, and total voltage will be 32.6VDC. Third, instead of using 3300uF, use 4700 or 6800uF/63VDC to reduce the ripple on higher currents (2-3A). The rest of the circuit is perfect. I like it cause it is so inexpensive and easy to make with those simple reconstructions i mentioned.

I was wonder if I insert the LM7809 into the circuit properly, I dont really understand words sometimes, and if i got it wrong I was wondering you could supply the correct schematic.  I cant buy any other IC listed in fixes expect a MC34072DG and know it wrong IC but it all I got :/

Link to post
Share on other sites

You forgot to connect the driver and output transistors to the power supply (the input of the 7809 regulator).

Ivan used the original circuit and most of its parts then added a 7809 regulator and an 18V zener diode so that the maximum unregulated supply voltage to the opamps is only (+27V plus the -5.6V negative supply=) 32.6V then the original opamps rated at 36V maximum can survive.
But then since the positive unregulated supply is 27V then the maximum output voltage from the project at 3A is only about 20VDC, not 30VDC.

An MC34072 is two MC34071 opamps in one case. The surface-mount package might get too hot because it is very small.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...