Hi all, am a newbie in electronics, can someone teach me how to interface a micro controller (Atmega32) which output +5vdc to switch a 12v relay using npn transistor. my transistor is D637 or C458. my problem is how will i prevent the 12v applied to the C (collector) from not appearing at the B (base) to damage my micro controller, it urgent please. thanks.

 

Check the top of page 8: http://www.picaxe.com/docs/picaxe_manual3.pdf Different uC, but same interface.
Looks like the max collector current rating for a 2SD637 and a 2S458 is 100mA. Do you know what the relay's coil current is?...part#?...link?

Ken

 

Thank you Ken, that was helpful.