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

[joecool85]

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]

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]

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]

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]

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]

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

 

[Roff]

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.

Yep - brain fart on my part.

 

[Edmond]

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]

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]

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]

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]

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]

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

 

[Nigel Goodwin]

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]

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.