Hi, I've got this system up and running where a series of modules =
containing 16F628 (running @ 20MHz) and individually fed by LM7805 =
(TO-220 package) are all run from the same 24VDC line (long run) coming =
from a switching supply. Each module also has an LM7806 for driving an =
R/C Servo motor. All my modules work fine except that the 7805s are =
running rather hot even though the R/C motors are pulling much more =
current from the 7806 than the little PIC is from the 7805. The 7806's =
temperature is ok though. At first I thought that it would only be =
necessary to heat-sink the motor's regulator but know I think I might =
have to do the same with the PIC's. I can almost burn my finger from the =
7805 ...

I understand that 24V isn't the optimal voltage to run the 7805 from if =
I intended to draw a lot of current from it but National's datasheet =
says that it can take up to 35V and considering the very low current =
consumption I don't understand why it is overheating. I suspected the =
length of my supply line but running a module even a few minutes on a =
short length gives the same result. Besides, the voltage drop is barely =
perceptible and I have pretty good wire gauge. Could my choice of caps =
for the regulators be causing the problem ? I have one 470uF 35V =
electrolytic before the 2 regulators and a 0.1uF ceramic cap after each =
of them.

thanks,

Tobie Horswill
thorswil@exmachina.qc.ca

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads