MJLorton Solar Power and Electronic Measurement Equipment Forum
General Category => General Discussion => Topic started by: Tony3dd on October 13, 2013, 01:34:05 PM
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Hi all, I have a very simple circuit here from the Make Electronics book. Basically it's the introduction to transistors. I understand that applying a small voltage to base is allowing the current to flow from the collector o the emitter, but why the two very different voltage drops? If I take a voltage drop between the collector, and the emitter I would think it would be somewhat close to taking the reading from the collector to the negative end of the LED, but it's not even close. The first reading is like .65mV, and the second is like 9.98V.I would think they should very close to the 9.98. Why is it not close seeing how the voltage is flowing between the collector, and emitter either way right? Naturally these voltages are when the button is pressed.
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I think you need to use ohms law to calculate the voltage drops at the various points in your circuit then all will become clear; also you really need to post a circuit diagram and show at what points in the circuit you are measuring.
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Why is it not close seeing how the voltage is flowing between the collector, and emitter either way right?
You might just be confused in that it's the 11.8mA of current that is flowing, and the voltage, is simply a measurement of the potential difference at 2 points in your circuit.
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Trouble is I was getting like 65mV between the the collector end of the 180ohm resistor. That should have read 12v. Found out I had the other end of the resistor plugged into the wrong rail so I wasn't picking up the plus side of the power. It's all good now. I guess that's how you learn.