[sdiy] Multiple LM317s - serial or parallel?

[Jay Schwichtenberg]

Couple of things.

For the 3 and 5 volt supplies I'd get a rough guess of the current and put
dropping resistors between them and the 15V supply. Play close attention to
the wattage of the resistor since they will dissipate some of the
power/heat. Those will allow the regulators to run cooler.

It maybe marginal using a LM317 for the 12V. Some people like having 3V
delta between the input and output (I think that's what the data sheet
specs) but I like 4V. These are cheap mass produced parts and I've seen
others and I've had problems with them. There are a number of LDO regulators
out there that require 1.5 to 0.5 V delta that will fill the bill.

Good soldering.
Jay S.

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Justin Owen
> Sent: Friday, November 06, 2009 1:32 AM
> To: SDIY List
> Subject: [sdiy] Multiple LM317s - serial or parallel?
>
>
> Hello,
>
> I have an LM317 in a TO-220 package outputting 12V DC from a 15V
> DC supply.
>
> I have a second LM317 in a TO-92 package outputting 5V DC and a
> third outputting 3V.
>
> My plan was to run the 5V off the 12V and the 3V off the 5V -
> which is working just fine. There's beefy caps on the 12V input
> and all three have diode protection and Tantalums on the outputs.
>
> Is there any reason why I should consider running all three
> LM317s off the main 15V DC supply?
>
> I'd all but made up my mind on this - but now I'm second guessing myself.
>
> Just checking...
>
> Thanks.
>
> Justin
>
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>