Re: [CAD_CAM_EDM_DRO] lm317

Hi,

Might be better to get a wall wart 5V supply, if you don't need much
current. Maybe it can be mounted inside the 24V supply case. With big
drops, you run the risk of a regulator shorting out, and getting an
excessive voltage on the 5V output. A crowbar on the 5V output would be
a good idea.

Alan KM6VV


Roy J. Tellason wrote:

> On Saturday 05 June 2004 08:08 pm, afogassa wrote:
>
>>Hi All,
>> I need to get 24 and 5v from the same transformer,I had in mind that
>>I could set one lm317 to 24v. than feed another lm317 and set that to
>>5v. The 24v would feed a relay card and the 5v a pic 18c452
>> I've searched on the lm317 application notes and haven't found any
>>thing like it,will it work?
>
>
> Yeah, it'll work, depending. What you need to watch for with any kind of a
> regulator like that is the power dissipation. Dropping from 24V to 5V is a
> drop of 19V, which means that even pulling only half an amp, say, you'll
> still be kicking out 9 watts as heat. If you *must* go with this setup then
> I'd suggest a dropping resistor at the input of the second regulator, to get
> that down some. But why *must* you use only one transformer?
>
> The big issue here is how much current you need at each voltage. Can you nail
> that down?
>
>