Subject:
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2n2907 transistors
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 20 Apr 1996 04:03:15 GMT
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Original-From:
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Jeff Keyzer <jkeyzer@calweb&nospam&.com>
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Viewed:
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2120 times
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I'm trying to build the h-bridge circuit posted on this list, and,
of course, I'm having problems. It simply doesn't work. So, in my efforts
to troubleshoot the thing, I'm trying to figure out how each part of the
circuit is supposed to work. Which brings me to my questions...
Alright. The 2N2907 is supposed to be a PNP metal can type
transistor. I've managed to get a few of them. First of all, it seems that
the pin diagrams in my Motorola databook aren't correct. I'm using my
multimeter to check the beta of the transistor, and the only way I can get
it to read a value is by making the lead closest to the tab the emitter, the
center lead the base, and the other lead the collector. (As opposed to
Base, Collector, Emitter, in that order, in the databook!) The transistors
then give me betas between 100 and 250, which are fine.
I'm trying to figure out if these transistors actually work by
constructing a test circuit which powers an LED. Right now, I've got the
led and a 1K resistor going between ground and the transistor's emitter. I
have connected the collector straight to positive. When I then connect the
base to negative, the LED turns OFF. When connected to positive, the LED
turns ON. Isn't this a little strange? The h-bridge circuit featured on
this mailing list says that when the base of the 2n2907 is connected to
ground, the transistor should turn ON. What's wrong here??? My
understanding of transistors is a little fuzzy, especially PNP transistors,
so maybe it's just me, but things don't seem to be coming together right
here...
Anyways, if anyone could help me out with this, I'd really
appreciate it. It's a little irritating to throw this circuit together,
connect power, and have NOTHING happen. Not even a puff of smoke, which
surprised me...
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