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Insulated Gate Field-Effect Transistors
39 questions By Tony R. Kuphaldt
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Question 34 of 39
Predict how this circuit will be affected as a result of the following faults. Consider each fault independently (i.e. one at a time, no multiple faults):
- Transistor Q1 fails shorted (collector-to-emitter):
- Transistor Q2 fails open (drain-to-source):
- Resistor R1 fails open:
- Resistor R2 fails open:
For each of these conditions, explain why the resulting effects will occur.
Reveal answer- Transistor Q1 fails shorted (drain-to-source): Motor runs all the time and will not turn off.
- Transistor Q2 fails open (drain-to-source): Motor refuses to run.
- Resistor R1 fails open: Motor refuses to run.
- Resistor R2 fails open: Motor runs when switch is pressed, takes a long time to turn off when switch is released.
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.
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Question 35 of 39
Predict how this circuit will be affected as a result of the following faults. Consider each fault independently (i.e. one at a time, no multiple faults):
- Transistor Q1 fails shorted (drain-to-source):
- Transistor Q2 fails shorted (drain-to-source):
- Resistor R1 fails open:
- Resistor R2 fails open:
- Solder bridge (short) past resistor R1:
For each of these conditions, explain why the resulting effects will occur.
Reveal answer- Transistor Q1 fails shorted (drain-to-source): Motor refuses to run.
- Transistor Q2 fails shorted (drain-to-source): Motor runs all the time and will not turn off.
- Resistor R1 fails open: Motor runs all the time and will not turn off.
- Resistor R2 fails open: Motor refuses to run.
- Solder bridge (short) past resistor R1: Motor runs when switch is initially unpressed (as it should), but transistor Q1 will fail when switch is pressed. This may cause the motor to stop running or to never stop, depending on how Q1 fails. The fuse may also blow as a result.
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.
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Question 36 of 39
A very useful MOSFET circuit is the bilateral switch, an example shown here for you to analyze:
The “dual inverter” circuit simply ensures the two control lines A and B will always be opposite polarities (one at Vdd potential, the other at ground potential).
What is the purpose of a “bilateral switch” circuit? Hint: there are two integrated circuit implementations of the bilateral switch - the 4016 and the 4066. Investigate the datasheets for these integrated circuits to learn more!
Reveal answerI’ll let you research this one yourself!
Notes:If your students have not yet learned about digital transistor circuits, this would be a good time to introduce the concept of “high” and “low” logic states, in this case as control signals to the bilateral switch cell.
Ask your students what the purpose of a bilateral switch might be, since we already have mechanical switches capable of switching almost any type of electrical signal known.
