You got caps on all inputs and outputs? could be oscillating.


----- Original Message -----
From: "Lucian" <luciffer@HOME.RO>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, May 15, 2004 8:27 AM
Subject: Re: [EE:] Cascading Regulators


> I put it next to a heatsink, but not tightly coupled, as it is
isolated.
> I hope it will not get too hot. My mistake in designing the circuit
and
> connecting the LM338 and LM7805 on the same heatsink.
>
> Now my problem is solved and the circuit is working nice, apart from
the
> 13.8V problem: I can't get 13.8V out of the LM338 regulator. The
adjust
> resistors are as follows: 220R between ADJ and VOUT and 2.2K plus a 5K
> potentiometer between ADJ and GND. Am I mistaking the values of the
> resistors ? If so, what would be some other better values ? (I have
smd
> resistors and I don't know how could I change them, but to know for
the
> future). Could the potentiometer be too bad ? As it jumps suddenly
from
> 13.3 to 14.6+.
>
> Lucian
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Russell McMahon
> Sent: 15 mai 2004 07:41
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE:] Cascading Regulators
>
> > ICs. Anyway, th maximum current is around 500mA through the 7805.
>
> (13.8 - 5 ) x 500 mA =~4.5w
> Not vast but heatsink accordingly.
>
>         RM
>
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