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My first power supply

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Tek Tech:

--- Quote from: james_s on April 28, 2019, 08:02:29 pm ---When I was about 12 I built a power supply with 3 7812 regulators in parallel, it may not be advisable to do but it did work and I used it regularly for about 20 years before I finally rebuilt it with a switchmode regulator. Ironically that blew up within a year.

So the point is, I wouldn't do something like that in a commercial product but sometimes you can get away with things.

--- End quote ---
I've done the same thing: stacking several 78xx in parallel for more Amps and less heat and it worked surprisingly well. I'd suggest, for best results they all should be from the same batch.

MarkF:

--- Quote from: Tek Tech on April 30, 2019, 01:43:50 am ---
--- Quote from: james_s on April 28, 2019, 08:02:29 pm ---When I was about 12 I built a power supply with 3 7812 regulators in parallel, it may not be advisable to do but it did work and I used it regularly for about 20 years before I finally rebuilt it with a switchmode regulator. Ironically that blew up within a year.

So the point is, I wouldn't do something like that in a commercial product but sometimes you can get away with things.

--- End quote ---
I've done the same thing: stacking several 78xx in parallel for more Amps and less heat and it worked surprisingly well. I'd suggest, for best results they all should be from the same batch.

--- End quote ---

If you put several regulators in parallel, you should put a series resistor on each output to limit the current due to small differences in the output voltage of each regulator.  Refer to example from the datasheet:

   

rsjsouza:
Good project and good looking supply - congratulations! Power supplies are always pretty cool as starting projects - I still remember the one I assembled with my dad in the 80's.

Back in the day we did not have access to quality fans, thus we had to rely on large heatsinks for the bypass transistors (large TO-3 2N3055). Hey, at least the power supplies were quiet.  :-X

As you progress, you may want to pay a visit to Tanner Electronics in Carrolton if you haven't yet been there. It has quite a great selection of parts for projects. BG Micro is another local store (in Garland) that also has a good selection - they are an online shop, but you can always save on shipping by arranging local pickup.

Tek Tech:

--- Quote from: MarkF on April 30, 2019, 02:29:20 am ---If you put several regulators in parallel, you should put a series resistor on each output...

--- End quote ---
Yes, I should, and I never did. But it worked quite well, trouble free. However, using chips by different manufacturers would definitely require resistors on the outputs.

BTW, I also did the trick building home-made light dimmers long ago. I would connect two triacs in parallel (straight, no resistors) to reduce the heat. It was very effective.

queennikki1972:
So, I did go back and add the protection diodes, green banana jacks tied to PE, larger heat-sinks and a larger transformer of 12v 1.8 amps. I did not use the adjustable pots as the LM7812 and LM7805 are not variable. I measured the ripple and it looks good. I am purchasing a electronic dc load after December so Ill be able to test the load. I've tested about .25 amp load and seems to run nice and cool.

I've since built a variable supply with LM317T and working on a dual adjustable supply of 1.5-60vdc. With each type I learn more. After I fully understand the linear supplies Ill try some switch-mode supplies or some built using IC's and Transistors.

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