Simple PSU question .....

[Minion]

Hi guys , I have a quick question .....

I have a 12v DC supply that can put out 500ma and I want to regulate down to 6.3v using a lm317 regulator and need to know if I can still get 500ma from the supply ??


Thanx guys .....

[nigelwright7557]

Yes.

[Minion]

Thanx Nigel ......

[counter culture]

...but the thermal resistance junction-ambient of the TO-220 case, which is probably the one you've got, is 50 degrees C/watt, and dropping nearly 6V @ 0.5A is nearly 3 watts, which'll make it temperature limit before it gets to 150 degrees above ambient, but be careful, because it'll give you a nasty burn. You'll need a heatsink.

[Minion]

Originally Posted by counter culture

...but the thermal resistance junction-ambient of the TO-220 case, which is probably the one you've got, is 50 degrees C/watt, and dropping nearly 6V @ 0.5A is nearly 3 watts, which'll make it temperature limit before it gets to 150 degrees above ambient, but be careful, because it'll give you a nasty burn. You'll need a heatsink.

Thanx ... I got lots of chunks of aluminum laying around that I can bolt the LM317 up to .....
I"m using it for a DC heater supply for a 6v6 tube amp so it will suck 450ma , I actually found a 9v DC 1A walmart that I stole the transformer from for this PSU so it should dissapate a bit less heat the 12v one ......

Thanx again .....

[DF96]

Why use DC heater for a 6V6? Are you using it as the first stage in a phono preamp??

[!]

The 9V, 1A supply is better for a second reason too, it would be operating at half capacity instead of near 100% as the 12V 500mA would.

Say 9VDC wart transformer rises in voltage a little while half loaded to 9.4V (random guess, fudging till you have a measurement), (9.4V - 6.3V) * 0.450A = 1.4W, it'd get hot enough that it would still be nice to have a small heatsink on it.

[Minion]

Originally Posted by DF96

Why use DC heater for a 6V6? Are you using it as the first stage in a phono preamp??

I"m using DC heaters because it is impossible to find a 6.3v transformer where I live and I have a box full of AC and DC adapters to scavange Transformers from......

I could just use a resistor to drop the AC down to 6.3v I suppose but figured I got lots of Diodes , capacitors and lm317 regulators so why not make a nice regulated DC supply ......
I"m going to be useing about 14,000uF of capacitance in the supply so it should be fairly clean DC from the supply .....

Thanx

[!]

you could just unwind some of the secondary from the 9V you have...

[Minion]

Originally Posted by !

you could just unwind some of the secondary from the 9V you have...

I wouldn"t trust myself to do that and not screw it up ......