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Differential Transistor Amplifiers
19 questions By Tony R. Kuphaldt
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Question 19 of 19
Predict how the operation of this differential pair circuit will be affected as a result of the following faults. Consider each fault independently (i.e. one at a time, no multiple faults):
- Resistor R1 fails open:
- Resistor R2 fails open:
- Resistor R3 fails open:
- Solder bridge (short) across resistor R3:
For each of these conditions, explain why the resulting effects will occur.
Reveal answer- Resistor R1 fails open: More current will be drawn from V1; if V1 sags as a result, Vout will decrease.
- Resistor R2 fails open: Vout will assume a voltage level approximately equal to V2 - 0.7 volts.
- Resistor R3 fails open: Vout saturates to V (positive supply rail).
- Solder bridge (short) across resistor R3: Vout saturates to within a few tenths of a volt from -V (negative supply rail).
Notes:The purpose of this question is to approach the domain of circuit troubleshooting from a perspective of knowing what the fault is, rather than only knowing what the symptoms are. Although this is not necessarily a realistic perspective, it helps students build the foundational knowledge necessary to diagnose a faulted circuit from empirical data. Questions such as this should be followed (eventually) by other questions asking students to identify likely faults based on measurements.
