# Find DC components of npn and pnp transistor

I'm sorry but I can't seem to figure this transistor question. The question goes as follows:

Draw a DC-circuit and determine the unknown component values. Which DC-voltages ( reference is ground) and DC-currents will be measured ?

simulate this circuit – Schematic created using CircuitLab

These are the values that are given

I can't seem to start anything with this problem using only the values given. I would appreciate some help, this is no homework but if you find that I haven't done enough to try and answer he question, it is ok is you close this question. I just don't know how to find the components using only those given

• If $I_{\text{C}_2}=2\:\text{mA}$, then why can't you calculate $U_{\text{E}_2}$? Isn't it obvious how to proceed to that value? (I'm assuming they want to know it, given that named line there.) Note that we are allowed to assume $T_2$ isn't saturated, so if you know it's collector current you also know its emitter current.
– jonk
Feb 2, 2020 at 18:59

It's a ridiculously useless circuit of the kind that only university professors seem to think exist.

Since 'beta' is 100, them Ib1=Ic1/beta. Same formula for transistor 2. From that you can calculate the 'biasing' resistors, taking Vbe ~ 0.6V.

All 'operating points' can then be calculated.

'Real' transistors however have a wide range of beta, so it's truly a poor circuit. I suppose it does at least show up those who were asleep in class.

I can't seem to start anything with this problem using only the values given.

Ok here’s a start. You want the collector voltage to be nominally half the DC supply voltage. That gives you the current through the collector resistors and, knowing beta it tells you the current into the base.

small print: it’s a crappy circuit in reality and nobody would use it outside of some test of ability to solve circuit problems.

• Ic1 and Ic2 are given, so the first part is not necessary. Vce1 is not in the middle of the rail, by design. Also, I like that the emitter resistor of the second transistor is called RC2... Feb 2, 2020 at 19:46
• @SredniVashtar good point. I never read the small print despite leaving some of my own. We’ll see if the op can pick up the pieces given that all I’ve really provided is encouragement. Feb 2, 2020 at 20:10