modified 9 years ago

LAoE 4N.6 Important transistor circuits

01:29:01

Top-left corner: Follower 
Vc = Vb - 0.6V

Top-right corner: Current source - fixed (the emitter resistor was added)
Ie = (V b -  V be) / R emitter 
(Variable resistor can be changed to show that Ic / I e is fixed)
https://en.m.wikipedia.org/wiki/Current_source (in the "Zener diode current source" section.)

Bottom-left corner: Amplifier
Ice is controlled by Vb. A current source with a "current sensing" collector resistor.

Bottom-right: The switch
Ib = 10 * Ice_min (base current 10x overdriven)

published 9 years ago

hurz

9 years ago

http://everycircuit.com/circuit/4865027882614784

hurz

9 years ago

Sorry, I have written a long lasting explanation why I made this modification to your current sink demo, but lost it while copy and paste 😩 .... hope you understand anyway 💡 keep it up!

2ctiby

9 years ago

The amp meter, being a very low resistance, is basically shorting out that pot in the top right circuit, making that pot in effect non-existent. An amp meter is meant to be in series, not across a component. Also....for the point you are trying to make here, I think that you need to have an emitter resistor in place.

jho_nth

9 years ago

I guess current source is wrong

nemethakos

9 years ago

Yes, the current source was not working. With the emitter resistor, it is now working and the current is set to 2mA.

hurz

9 years ago

Yes, and 738mVbe without an extra emitter resistor results also in 2mA and is as basic circuit better understanable I guess. But for a more practical use an emitter resistor is a good idea for stability

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