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0-30V Stabilized Power Supply


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Hi all

First time for me on this site. I have built this and it works grate. By the way very new to electronics, I have started it as n hobby at 34 (last year). I want to built the two vertions off the amp/volt meters the show with the project. where can i find the scematics and so on for the bords shown and could some one please tell me in laymens terms how the second lcd display one works.  Would epreciate it.

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How i have to connect it ? how its right ? how i can get +-30V ?

This ?                                           OR              This?
_Supply1_              _Supply2_                 _Supply1_             _Supply2_              
|               |          |               |            |               |         |               |
|               |          |               |            |               |         |               |
|               |          |               |            |               |         |               |
|_+____- __|          | __+__-__ |            |_+____- __|         | __-__+__|
   |         |__________ |     |                   |         |____________|     |
   |                 |               |                   |                   |                |
   |                 |               |                   |                   |                |
   |_Voltage?___|_Voltage?_|                   |_Voltage?____|_Voltage___|

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The answer is
Supply1_              _Supply2_                     
|                  |          |                  |         
|                  |          |                  |           
|                  |          |                  |           
|_+____- __|          | __+__-__ |       
    |        |__________ |    |             
    |                |              |                 
    |                |              |               
Good luck!   

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Hi can I use the op amp LF355 instead MC34071 or TLE2141? i saw that Vcc max is 44. thx

The National Semi LM355 is obsolete and has not been made for 11 years. Its max allowed supply was only 36V but was 44v for the more expensive LF155.

They will not work in the latest circuit because their input common-mode range does not go as low as the MC34071 or the TLE2141. The LF355 is almost the same as a TL081.
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  • 3 weeks later...

Hello everyone.
I saw all posts, but my english is poor, so if i will be repetitive, i'm so sorry in advance.
I would like to make this PS and i have the pcb for old version maked yet and all components, and found now this discussion about "problems" of original version. I understood, one of the problems are some components like 2N2219 over-heats, but i just need 24v and 2,5A max, so i have one transformer of 24V - 3A. This is critical for this values? I can change too:
R1 = 2,2 KOhm 2W
R2 = 82 Ohm 2W
R7 = 0,47 Ohm 10W
For dissipate more heat and dont burn.
So only with this changes i can make the old version without burn problems?
Note: I don't need the 30V 3A max, just 24V 2,5A is enough for me.

Thanks in advance and sorry for my bad english.

My best regards,

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Replace the tiny 2N2219 driver transistor with a BD139 power transistor on a proper heatsink.

For an output of 2.5ADC the 24V transformer must deliver 33.9V at 2.5A which is 84.8VA. Then a 24V/3.5A transformer must be used.

The original TL081 opamps have a max allowed total supply voltage of 36V. But with a 24V transformer two opamps have a total supply of 41.7V without a load. 44V opamps are available.

The single 2N3055 output transistor must dissipate 36V at 2.5A when the output is shorted and set to 2.5A. This is 90W which will overheat the transistor even if it has a huge heatsink.
It needs two output transistors to share the heat.

The offset voltage adjustment parts are wrong and connect to the wrong voltage. 

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Hi Zsyt,
The transformer specified in the original project is overloaded and might cause trouble.
The 24VAC is rectified and has a peak voltage of 34V. Then if the output has a load of 3A the transformer must provide 34V x 3A= 102VA.

The voltage on your transformer is too low at 22V and will have a peak voltage of 31V. Then your transformer is overloaded if the DC current from the project exceeds 1.9A.
Your max output voltage at 1.9A will be about 22.5V.

The fuse should blow if the transformer is overloaded. 60VA/230V= 0.26A. Maybe use a slow blow 0.3A fuse.

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