Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!apple!usc!merlin.usc.edu!nunki.usc.edu!cyamamot
From: cyamamot@nunki.usc.edu (Cliff Yamamoto)
Newsgroups: sci.electronics
Subject: How can I turn on this bulb with TTL?
Keywords: NPN, TTL, bulb, 12 volts, bias
Message-ID: <4363@merlin.usc.edu>
Date: 13 Jul 89 13:42:46 GMT
Sender: news@merlin.usc.edu
Reply-To: cyamamot@nunki.usc.edu (Cliff Yamamoto)
Distribution: na
Lines: 18

Greetings,
	I know this is a simple circuit, but I can't seem to get the bias
right or something.  The circuit is as follows :

		  C----bulb---> + 12 volts
TTL---1 Kohm----B				NPN transistor
		  E---+
		      |
		     GND

The problem is when the TTL is high, the bulb barely lights up.  This circuit
is for automotive use so the bulb is just an instrument panel bulb (not a high
powered spot light).  Isn't 2N2222 or 2N3904 good enough for this?  How does
one go about selecting a transistor for this?  And lastly, how does one figure
out the bias needed to fully turn it on?

Thanks for all your EE101 advice!  :)
Cliff Yamamoto