Constant current source-Transistor

131

02:31:45

Change the voltage of the LED, below 4v because it is the supply voltage

Calculation:
Vbb=Vcc=4V
Ic=10mA, β=100
Just by using a perfect resistor on base and adjusting base current, we can decide the Collector current

β=Ic/Ib, since we know Ic and β,
Ib=Ic/β=10mA/100=100μA
Now, Rb(the base resistor) =(Vbb-Vbe) /Ib
=(4V-0.8v) /100μA=32kΩ

Since the Vbb is close to the knee voltage of silicon diode approximately 0.7V, i chose 0.8V
Now if you vary the Vled from 1v to 4V, The LED won't breakdown 
Don't vary the Vbb voltage, just change the Led turn on voltage or knee voltage

published 11 months ago

BraydanD

11 months ago

Nice calculations, however in practice the transistor would heat up and draw more current in a runaway effect, eventually burning out, how would you fix this?

jbasanth

11 months ago

In your case, the transistor will break down Or burn out eventually as you said. We can use higher rated transistors or a protection circuit

jbasanth

11 months ago

I am currently studying transistors and i only intended to create a current source

jbasanth

10 months ago

Instead use Emitter biased Driver

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