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Electronics => Electronics => Topic started by: joe61 on April 13, 2011, 04:59:13 PM

Title: Need to be smarter than the transistor
Post by: joe61 on April 13, 2011, 04:59:13 PM

I'm trying to understand transistors. In that effort I ordered some stuff to try to build an H-bridge as described at http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-impl.html (http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-impl.html)

The transistor is a TIP 107 PNP. The data sheet linked to from Digi-Key ( http://www.onsemi.com/pub_link/Collateral/TIP100-D.PDF (http://www.onsemi.com/pub_link/Collateral/TIP100-D.PDF) ) doesn't give the pin functions, but I'm assuming that pin 1 is base, 2 is collector and 3 is emitter, is that right?

I'm stuck on the first little schematic at the top of that page. I might be misunderstanding the schematic and wiring it incorrectly, I'm not sure. I have a 10K pullup resistor on the base so that current should not flow between collector and emitter. It does. If I move the resistor to pulldown, the LED still lights up.

I'd appreciate a pointer if someone here sees what I'm doing wrong.

Thanks

Joe

Title: Re: Need to be smarter than the transistor
Post by: MikeK on April 13, 2011, 05:15:34 PM

You've got the pinout correct, but the emitter is the leg with the in-pointing arrow, not the collector.  You've got them switched.

Also, you need a current limiting resistor at the base that you switch to ground.

Title: Re: Need to be smarter than the transistor
Post by: joe61 on April 13, 2011, 06:46:52 PM

Thanks very much, I didn't understand about the collector and emitter changing places.

Joe

Title: Re: Need to be smarter than the transistor
Post by: vinniewryan on April 13, 2011, 07:37:29 PM

http://www.satcure-focus.com/tutor/page4.htm (http://www.satcure-focus.com/tutor/page4.htm)

this is a very good explanation of how they work, and it has a schematic symbol that shows you the correct Base, Emitter, and Collector.

Cheers!

Title: Re: Need to be smarter than the transistor
Post by: MikeK on April 13, 2011, 08:06:07 PM

This is another good explanation of transistors: http://www.rason.org/Projects/transwit/transwit.htm (http://www.rason.org/Projects/transwit/transwit.htm)

Title: Re: Need to be smarter than the transistor
Post by: joe61 on April 14, 2011, 05:37:18 AM

Thanks guys, appreciate it.

Joe