Electronic – Odd BJT circuit

biasbjt

This circuit came in my today's exam. It asked to find every base, emitter and source current.Base emitter voltage .8 and \$\beta\$ for both BJT is 49.

first I tried normally where \$I_B\$ found that it is coming out from n type BJT and go into p type BJT which is not possible.

schematic

simulate this circuit – Schematic created using CircuitLab

I also try for \$Q_p\$ saturation \$Q_n\$ active ; \$Q_n\$ saturation \$Q_p\$ active and both saturation. Every time I've found some impossible values which cancel that option.
same thing happen to my other friends.

Is there any other condition I didn't consider?
Is there any other situation or special situation happen?

Best Answer

The collector junction of Qp and emitter junction of Qn - forward biased.

The collector junction of Qn and emitter junction of Qp - reverse biased.

now the base current of Qn is, $$I_{Bn} = \frac{V_1 - V_{BEn} - V_{CBp}}{R1+R5+(\beta+1)R4}$$ then, $$I_{Cn} = \mathrm{min}(\beta I_{Bn}, I_{Csat})$$ where $$I_{Csat} = \frac{V_1-V_{CEn}}{R_4+R_3}$$

The voltages you can calculate as.

$$V_{En} = R4\times(I_{Bn}+I_{Cn})$$ $$V_{Cn} = V_1 - R3\times(I_{Cn})$$ $$\text{so on ...}$$