If you change to USB, maybe you can do without the external
power and generated the target Vpp with a step-up boost
converter or charge pump. 

At least you can supply the 18F2550 with USB power
and supply the rest of the +5V from the 7805. In that case,
the current consumption of the 7805 should be lower
than the original Warp13a.

Regards,
Xiaofan

-----Original Message-----
From: Jim Robertson [mailto:jimpl@newfoundelectronics.com]
Sent: Wednesday, October 19, 2005 4:48 AM
To: piclist@mit.edu
Subject: [EE] TO-92 volt regs and heat issues

Greetings Piclisters.

I currently have a 78L05 (100mA) in the WARP-13 but with the possible 
change over to USB via a 18F2550 it tends to run just a little hot.

My question  is if I change it over for a Zetec ZSR500C that is rated 
for 200mA does it follow that the output drive is lower impedance and 
therefore if I draw the same amount of current from it, it would not 
generate as much heat as the 78L05? Right/Wrong?

I am also looking at adding a heatsink if I can find a suitable size 
and shape. Any other ideas or solutions anyone. Thanks for any help.

Regards,

Jim
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