MP3Car.com - View Single Post - AVR based laptop startup/shutdown controller

Rob Withey · 03-27-2008, 07:25 AM

Quote: Originally Posted by Shad0wca7

Actually I forgot to add them for the relays!

What I meant on my previous post was possible transients coming from the actual car power source which the transistor will be connected to?

If you're not comfortable designing with transistors then stick with the relays.

I don't know what you are referring to with the transient thing. Just get a transistor that can handle sufficient Vce (assuming bipolar) involved. I'd switch that relay with an NPN bipolar with the emitter grounded, suitable base resistors and relay coil between the collector and power source. When the base saturates, the collector goes to about 1 diode drop above ground and the relay switches. Whatever you do, don't go for an emitter-follower when switching with logic levels - big waste of time.

Actually, I wouldn't (and didn't) swtch a relay. I use a high side driver.

03-27-2008, 07:25 AM	#6
Rob Withey Raw Wave Rob Withey's CarPC Specs Join Date: Apr 2000 Location: Surrey, UK Vehicle: '97 Vauxhall Corsa 1.5 TD Posts: 1,965 My Photos: ()	Quote: Originally Posted by Shad0wca7 Actually I forgot to add them for the relays! What I meant on my previous post was possible transients coming from the actual car power source which the transistor will be connected to? If you're not comfortable designing with transistors then stick with the relays. I don't know what you are referring to with the transient thing. Just get a transistor that can handle sufficient Vce (assuming bipolar) involved. I'd switch that relay with an NPN bipolar with the emitter grounded, suitable base resistors and relay coil between the collector and power source. When the base saturates, the collector goes to about 1 diode drop above ground and the relay switches. Whatever you do, don't go for an emitter-follower when switching with logic levels - big waste of time. Actually, I wouldn't (and didn't) swtch a relay. I use a high side driver. __________________ 6yr old first install died 20/8/2005 as result of bad bios flash. New system : 6x5x2" contains 1GHz C3 PCM9373, ISR based PSU, 512Mb flash DOM, 8Gb CF HDD, 98Lite, DirectShow based frontend. GPS : Rikaline 6010. Display : LTM08C351 + LVDS receiver.