Basic switching transistor

134

02:31:55

This circuit demonstrates the usage of an NPN transistor as a switch, the LED will only flow if the switch in the circuit is closed.

published 12 years ago

rbrtkurtz

12 years ago

I'm not entirely sure what you've got going on with those 1K resistors there, but they're wasting energy. Your circuit is drawing over 27mA total. If you swap those two 1Ks for 10Ks, make a voltage divider out of them (run them in series from the switch to ground), then hook up the base of your NPN in between those two resistors (4.5V), your circuit will be much more efficient. The same amount of current will be flowing through the LED (10.3mA with that 680 resistor), but your circuit will now only be using 11.1mA total. That's nearly a third of what it was using!

sBoff

12 years ago

Rbrtkurtz, no offence, your point is valid however, this is obviously targeted at a novice.. I dont think a novice would care or follow what you are talking about. The illistration is perfect for it's target audience.

rbrtkurtz

12 years ago

If you're at the point where you're learning about transistors, you should already understand a voltage divider. Why complicate things more than they need to be if your audience is novice? Get rid of the 1K pull-down resistor. The example still works perfectly, it's only using about 2/3 the power, and there are less parts. This circuit works as an example, yes, but I really wouldn't call it perfect.

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