amplifierbiasbjtcircuit analysis
I'm trying to bias the bjt amp with two voltage sources and make the collector of bjt at 0.5V to maximize output swing but the simulation give me too much different result, why? The collector current I choose – 5ma, R4 voltage drop – 1V, XMM1 shows 3.6V
The MMUN2211LT1 already has a base resistor of 7~13kΩ with an hFE of 35 ~60.
If you apply 2.5V to base resistor it will saturate to 0.2Vmax with 5mA collector current.
added- - I read the above in the product spec. Have you read it? My analysis of this switch is as follows; Output 5mA for input 2.5V/10kΩ nom = 0.25mA which translates to current gain of 20x which is typical for a saturated switch. 5x is common for high current switch.
So apply more base voltage to this device and remove the external base resistor.
The DC analysis isn't that difficult.
EDIT: I see a far simpler analysis:
\$I_{B1} = \dfrac{V_{C1} - V_{BE2} - V_{BE1}}{R_2 + P_2}\$
\$V_{C1} = 9V - I_{C1} \cdot R_3 = 9V - \beta I_{B1} \cdot R_3\$
\$ \rightarrow I_{B1} = \dfrac{9V - V_{BE2} - V_{BE1}}{R_2 + P_2 + \beta R_3}\$
Now:
\$I_{E2} \approx \dfrac{V_{C1} - V_{BE2}}{R1}\$
\$V_{C2} = 9V - I_{C2} \cdot R_4 \$
Assume a value for the base-emitter voltages and P2 ,solve for the collector currents and check for active/saturation operation.
Best Answer
Can you use adaptive biasing, like this
simulate this circuit – Schematic created using CircuitLab