Calculating currents from this circuit

[Englewood]

Hello,

I would like to know how do I calculate the current of the base and the collector of this circuit form the Voltages.

 

[code_slave]

This looks like your picture:

http://www.learningaboutelectronics...calculate-the-base-current-ib-of-a-transistor
http://www.learningaboutelectronics...late-the-collector-current-ic-of-a-transistor
http://www.learningaboutelectronics...culate-the-emitter-current-ie-of-a-transistor

 

[Audioguru]

You need to learn about the base to emitter voltage of a turned on transistor. It is about 0.7V. The datasheet for the BC108 transistor shows that it is typically 0.7V when its collector current is about 10mA and its base current is about 0.5mA.
Then simple arithmetic is used to find the voltage across the 22k base resistor which is 9V - 0.7V= 8.3V.
Ohm's Law is used to simply calculate the base current which is 8.3V/22k ohms= 0.377mA.

But we do not know the color of the LED so we do not know its forward voltage. Assuming that it is a 1.8V red LED and assuming that the collector to emitter voltage of the turned on transistor is 0.1V then the 330 ohm resistor has a voltage across it that is (9V - 1.8V - 0.1V)= 7.1V. Ohm's law is used again to simply calculate the collector current that is 7.1V/330 ohms= 21.5mA.

Maybe it is a 3.3V blue LED. Then the 330 ohm resistor has a voltage across it that is (9V - 3.3V - 0.1V)/330 ohms= 5.6V. YOU calculate the collector current.

 

[Englewood]

Thank you for the information.

I have been thrown in at the deep end with an electronics level
3 course.

So it's all a new learning curves for myself

 

[Englewood]

The LED is this one
https://uk.farnell.com/dialight/521-9628f/led-3mm-red-grn/dp/1461589?Ntt=146-1589

Does the Data sheet tell you the collector to emitter voltage of the turned on transistor ?

This is the trans
https://www.farnell.com/datasheets/296633.pdf

 

[Audioguru]

The LED is this one
https://uk.farnell.com/dialight/521-9628f/led-3mm-red-grn/dp/1461589?Ntt=146-1589

It has two LEDs inside and each one is different. Will you use the red one or the green one?

Does the Data sheet tell you the collector to emitter voltage of the turned on transistor?

I think "Multicomp" is not a manufacturer, I think it is a re-seller and its datasheet has no "typical" graphs.
I have a 1968 databook from Philips that shows a graph of the saturation voltage of an obsolete old BC108 transistor that is typically 0.1V when its collector current is 20mA and its base current is 1mA.

 

[Englewood]

Its a green one

 

[Englewood]

When you calculated the base current

did you divide 8.3 by 22000 as its a 22 k res?

 

[Audioguru]

When you calculated the base current did you divide 8.3 by 22000 as its a 22 k res?

Of course, as I explained in post #3:
"Then simple arithmetic is used to find the voltage across the 22k base resistor which is 9V - 0.7V= 8.3V.
Ohm's Law is used to simply calculate the base current which is 8.3V/22k ohms= 0.377mA."