Jump to content
Electronics-Lab.com Community

0-30V Stabilized Power Supply


Recommended Posts

Thanks audioguru, I read the answers about to use two 2n3055. Will one BD139 be able to support both tranzistors ?

Yes because each output transistor has half the total current then their current gain is higher so the BD139 driver uses less current and is cooler. Even the opamp that drives the BD139 will use less output current and will be cooler.
Link to comment
Share on other sites

i have a problem about my voltage adjust(potentiometer), the problem is that the voltage is not balance and not linear, my minimum voltage is 0.7v and max with 32v, but if i adjust the potentiometer 1/2 the voltage is only 1.3v, in 3/4 of my potentiometer i can adjust the voltage properly start by 3v-32v but i really wonder why the voltage is gather in the 3/4 of my potentiometer???? i use 10k pot, i already replace it 3x,, but the same thing happened., i also replaced it with 1k value, but the max voltage lower, only 7.4v,,.. can you help me sir???thank you!!

Link to comment
Share on other sites

Hi Audioguru
I have had a lot of trouble sourcing the shunt resistor (0R27 ohm) for the 5A version in Australia, nearest is 0R22, 10W, or 0R33 10W.

But in the process I think I have ordered the wrong digital voltmeters (0 - 99V 3 wire) for the current display.  Since the volt drop across the shunt will only be just over 1V at 5A it will hardly register, and at 100mA, no chance.
Any ideas how I can fix the display problem?  And can I use the 0R33 shunt resistor? 

Link to comment
Share on other sites

It looks fine, although I'd say C1 is probably a bit undersized to expect a ripple free output at 3A. I'd recommend increasing C1 to 68,000uF or more.

The regulator will probably overheat and shut down, if you attempt to draw the full 3A, at lower voltage settings. A possible solution is to use a centre tapped transformer and tap changer to reduce the voltage to the regulator, at lower voltage settings.

Link to comment
Share on other sites

hi from brazil!
i didnt understand witch connection i have to do with the legs of the trimpot witch the u2 (i am using the mc4071) and it doesn t have the connection like the tl081 ...number 1 and 5 ...sorry for my english and simple problem with electronic... thanks

The datasheet for the MC34071 opamp shows its 10k ohms input offset voltage trimpot connected to pin 1, pin 5 and the negative supply almost the same as a TL081 opamp.


Link to comment
Share on other sites

Good Day!
I assembled the original schematic.My problem is that the rectifier out turns to be more than 24V, around50V (unusual because the secondary output of transformer I had is 24V. The second problem is at U1 pin 6 output voltage is around 19V instead of 11.2V. The third problem is  P1 and P2 has no effect when I turn the knobs.so the  measured VDCout is the same as around 50V. Any suggestion will be appreciated.

Link to comment
Share on other sites

Good Day!
I assembled the original schematic.My problem is that the rectifier out turns to be more than 24V, around50V (unusual because the secondary output of transformer I had is 24V

Why is that unusual?

It's what you should expect.

24V is the RMS voltage, when fully loaded, the peak will be 34V, fully loaded, but when open circuit the voltage will be up to 20% higher so 50V sounds reasonable.
Link to comment
Share on other sites

Cheap transformers have poor voltage regulation.

A Hammond 30V/4A transformer is 30V RMS at 4A. With no load its output voltage is 31.5V RMS so it has pretty good voltage regulation probably because it is huge and its windings have a low resistance.

I have a little Chinese 9V/100mA wall-wart power supply.
Its voltage is 9V when loaded with 100mA but its voltage is 18.5V (more than double!) when it has no load. It gets hot with and without a load. It is very cheap.

The TL081 opamps in the original project have an absolute maximum total supply of 36V.
The opamps in my fixed version of this project are rated at 44V. Their negative supply is only -1.3V.

24VAC has a peak of 33.9V which is reduced to 32.5V by the unloaded bridge rectifier. Then some of the opamps have +32.5V and -5.6V for a total supply of 38.1V if the transformer voltage does not rise without a load.
Of course the transformer voltage will rise without a load and blow up the opamps.

Link to comment
Share on other sites

We seem to have lost the extensive discussion on this power supply topic.    I attached what I believe is the latest version.   I could not find the updated parts lists to attach.    

UPDATE 12/30/09     Added parts list and Eagle file for double sided board  (Shown in photo below)

is this the updated shematic and partlist sir? thank you..
Link to comment
Share on other sites

  • 3 weeks later...

No, this is the most recent parts list / circuit diagram: http://www.electronics-lab.com/forum/index.php?topic=19066.msg1010703#msg1010703

I really think someone should update the frontpage to the most recent version. That way everyone would find the most recent version of the circuit and it would also stop the people from asking the same question over and over again.

Link to comment
Share on other sites

furthermore does exist any info of what all these (5 variable resistors) do in the final version ?

There are only two variable resistors, the same as in the original version:
P1 sets the output voltage.
P2 sets the maximum output current.

There are three trimpots that are adjusted only one time:
RV1 is the same as in the original version and adjusts the output offset voltage to zero when the voltage pot is set to zero.
The 20k voltage calibration trimpot in series with R11 is adjusted for an output of 30.0V when the voltage pot is at maximum.
The 100k current calibration trimpot in series with R18 is adjusted for a maximum output current of 3.0A when the current pot is set to maximum.
Link to comment
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...