Hello,

The circuit is given below which is about the triode--8050's working problems I would like to ask..In this circuit ,the pressure drop of the lamp is 9v while the working current is 60mA. It required that using constant current to work. Calculting the value of R3 and R1.

The voltage of pin13/14/15 when ULN2003 on is 0.7V , the voltage of triode base b is 3.1V and the c is 3V. The voltage of emitter is 2.4V.

The questions:

1). Is the R3 =(2.4-0.7)/0.06?

2) If the triode is in the saturation region ,shouldn’t the ce pressure drop be 0.3v? Why it’s 0.7v here?

3) If the work is in the amplifier region,how to guarantee that lamp work in the constant current--60mA ?

4) What references related to stable diode should I note when calculating the value of R1?