[aprssig] Tracker power control relay

James Jarvis jj at aprsworld.net
Mon Jul 19 13:53:49 EDT 2004

Scott - consider using a high side switching FET instead. IRF has some cute 
little parts that are pretty cheap. 5 amps in an SO-8 package for < $2 or 100 
amps in a TO-220-5 package for < $6. Logic level input. I can dig up some 
part numbers if you would like.

I did this on one of my weather stations a few years ago. It would power up 
the TNC and radio for 30 seconds whenever it wanted to transmit. After power 
up it would wait about 10 seconds for the KPC-3 to boot and the radio to 
stabilize, then it would send the packet and allow the KPC-3 20 seconds to 
get access to the channel and transmit.

I'm actually doing printed circuit board layout today on a similar board. It 
is (more-or-less) four IRF3310 100 amp high side switches, an Allegro hall 
effect current sensor, a PIC microcontroller, some LEDS, and some connectors. 
The IRF3310's include over current protection and shutdown, so in this 
application there will not be any fuses. 


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