Building a 12v 3amp power supply, parallel 7812s?

joecool85 · Mar 18, 2006

I've read online that you can parallel the 7812 regulators to get more amps:
**broken link removed**

With the resistors, do I have to use 4 - 1ohm resistors, or would one large 0.25ohm be alright? Also, is this the best way to get a 3amp power supply or should I be looking at a different design? This one looks easy, and I like that

Nigel Goodwin · Mar 19, 2006

joecool85 said:
I've read online that you can parallel the 7812 regulators to get more amps:
**broken link removed**

With the resistors, do I have to use 4 - 1ohm resistors, or would one large 0.25ohm be alright? Also, is this the best way to get a 3amp power supply or should I be looking at a different design? This one looks easy, and I like that

You could use one larger 0.25 ohm, generally though the reason for using four smaller resistors is cost, it 'may' be cheaper for four small resistors than one large one?.

This simple design has the advantage that the 7812's are still current limited, you can use a single transistor to give more current from a 7812 (example in the datasheet I seem to remember?), but this stops the current limiting working.

Be aware you will require substantial heatsinking!.

Edmond · Mar 19, 2006

joecool85 said:
I've read online that you can parallel the 7812 regulators to get more amps:
**broken link removed**

With the resistors, do I have to use 4 - 1ohm resistors, or would one large 0.25ohm be alright? Also, is this the best way to get a 3amp power supply or should I be looking at a different design? This one looks easy, and I like that

You can buy 7512T with 3A current limiting (metal package).

Edmond

Roff · Mar 19, 2006

Keep in mind that 0.25 ohms in series means your output voltage changes by 0.75V from no load to 3 amps load. If your load is nearly costant, this won't be a problem.

Nigel Goodwin · Mar 19, 2006

Ron H said:
Keep in mind that 0.25 ohms in series means your output voltage changes by 0.75V from no load to 3 amps load. If your load is nearly costant, this won't be a problem.

Not by that much, the 0.25 ohm is per regulator, each of which shares the current - so with five regulators the current through each 0.25 ohm will only be 600mA - so there will only be 0.15V drop.

joecool85 · Mar 19, 2006

I can readily get the 1A chip, but can't even find the 3A version online, any help?

Roff · Mar 19, 2006

Nigel Goodwin said:
Ron H said:

Keep in mind that 0.25 ohms in series means your output voltage changes by 0.75V from no load to 3 amps load. If your load is nearly costant, this won't be a problem.

Click to expand...

Not by that much, the 0.25 ohm is per regulator, each of which shares the current - so with five regulators the current through each 0.25 ohm will only be 600mA - so there will only be 0.15V drop.

Yep - brain fart on my part.

Edmond · Mar 19, 2006

joecool85 said:
I can readily get the 1A chip, but can't even find the 3A version online, any help?

What do you want to use it for?

joecool85 · Mar 19, 2006

The only use I have for it right now is powering a keyboard I have, but later on I'd like to use it for other things. The reason I want 3amps is because I have a transformer that is 12.6v @3amps and I want to take full advantage of it.

gerty · Mar 19, 2006

Here's one
https://jameco.com/webapp/wcs/store...toreId=10001&catalogId=10001&productId=192284
It's a 5 amp adjustable, to-220 case for $1.99

joecool85 · Mar 19, 2006

Where can I get the schematic on how to adjust it, and also, is there one that is just set at 12v for 5A?

gerty · Mar 20, 2006

If you look at the data sheet in the link it'll give you the info. Yes they also have a fixed 12v regulator in several different amp ranges. I personally like to keep a couple of adjustable regulators on hand, so that no matter what voltage I need (within the specs ) I'll have a regulator.
Hope this helps

joecool85 · Mar 20, 2006

Ok. I'll check out the datasheet. I couldn't find the fixed 12v regulator for more than 1A.

Nigel Goodwin · Mar 20, 2006

joecool85 said:
Ok. I'll check out the datasheet. I couldn't find the fixed 12v regulator for more than 1A.

You've never mentioned it so far, but what are you wanting to do?.

joecool85 · Mar 20, 2006

joecool85 said:
The only use I have for it right now is powering a keyboard I have, but later on I'd like to use it for other things. The reason I want 3amps is because I have a transformer that is 12.6v @3amps and I want to take full advantage of it.

Building a 12v 3amp power supply, parallel 7812s?

joecool85

Member

Nigel Goodwin

Super Moderator

Edmond

Member

Roff

Well-Known Member

Nigel Goodwin

Super Moderator

joecool85

Member

Roff

Well-Known Member

Edmond

Member

joecool85

Member

gerty

Member

joecool85

Member

gerty

Member

joecool85

Member

Nigel Goodwin

Super Moderator

joecool85

Member

Similar threads

Building a 12v 3amp power supply, parallel 7812s?

Member

Super Moderator

Member

Well-Known Member

Super Moderator

Member

Well-Known Member

Member

Member

Member

Member

Member

Member

Super Moderator

Member

Similar threads

Privacy & Transparency

Privacy & Transparency