Sunday 19 March 2017

Calculating resistance in a circuit where relay is controlled by microcontroller


enter image description here


I've been asked to calculate the theoretical resistance of R1 in the shown circuit. The information that I've been given is that the relay needs 60 mA and 12V. I've also been told that the transistor's hFE/Beta value is 20 and that the voltage drop between the base and emitter is 0.7 V. I've tried calculating the resistance of R1, but when I do I don't seem to use all of the information given which leads me to believe that I am doing it wrong. Furthermore, I am a bit confused as to what is meant by the term theoretical resistance of R1.


If anyone could lead me in the right direction I would greatly appreciate it.




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