DT002
Industrial Electronics
Review Questions - I
1. The basic semiconductor amplifying device is a:
a. diode
b. transistor
c. pn-junction
d. silicon gate
2. The voltage drop across a silicon signal diode when conducting is about:
a. 0.3V
b. 0.6V
c. 0.7V
d. 1.3V
3. A bipolar transistor has three terminals named:
a. base, emitter and drain
b. collector, base and source
c. emitter, base and collector
d. drain, source and gate
4. The three leads from a PNP transistor are named the:
a. collector, source, drain
b. gate, source, drain
c. drain, base, source
d. collector, emitter, base
5. A low-level signal is applied to a transistor circuit input and a higher-level
signal is present at the output. This effect is known as:
a. amplification
b. detection
c. modulation
d. rectification
6. The type of rectifier diode in almost exclusive use in power supplies is:
a. lithium
b. germanium
c. silicon
d. copper-oxide
7. In a forward biased pn junction, the electrons:
a. flow from p to n
b. flow from n to p
c. remain in the n region
d. remain in the p region
8. The following material is considered to be a semiconductor:
a. copper
b. sulphur
c. silicon
d. tantalum
9. A semiconductor is said to be doped when small quantities of the following
are added:
a. electrons
b. protons
c. ions
d. impurities
10. The connections to a semiconductor diode are known as:
a. cathode and drain
b. anode and cathode
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DT002
Industrial Electronics
Review Questions - I
c. gate and source
d. collector and base
11. Bipolar transistors usually have:
a. 4 connecting leads
b. 3 connecting leads
c. 2 connecting leads
d. 1 connecting lead
12. A semiconductor is described as a "general purpose audio NPN device". This
is a:
a. triode
b. silicon diode
c. bipolar transistor
d. field effect transistor
13. Two basic types of bipolar transistors are:
a. p-channel and n-channel types
b. NPN and PNP types
c. diode and triode types
d. varicap and zener types
14. A transistor can be destroyed in a circuit by:
a. excessive light
b. excessive heat
c. saturation
d. cut-off
15. To bias a transistor to cut-off, the base must be:
a. at the collector potential
b. at the emitter potential
c. mid-way between collector and emitter potentials
d. mid-way between the collector and the supply potentials
16. Is this diode forward-biased or reverse biased?
17. Insert a diode into this circuit schematic in the correct direction to make it
forward-biased by the battery voltage:
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DT002
Industrial Electronics
Review Questions - I
18. A student sets up a circuit that looks like this, to gather data for characterizing
a diode:
Measuring diode voltage and diode current in this circuit, the student generates
the following table of data:
a. Sketch the diode characteristic curve in the region 0.6 V < Vdiode <.8 V
b. Write out the load-line equation for the diode if the potentiometer is set
to 5 kΩ.
c. Plot the 5 kΩ load-line on the same graph as the characteristic curve
d. Determine the diode current.
19. How is it possible to determine the polarity of a rectifying diode (which
terminal is the anode, and which terminal is the cathode) from its physical
appearance?
20. Complete the following table of values for this diode circuit, assuming a
typical forward voltage drop of 0.65 volts for the diode:
21. Complete the following table of values for this diode circuit, assuming a
typical forward voltage drop of 0.65 volts for the diode:
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DT002
Industrial Electronics
Review Questions - I
22. Predict how all component voltages and currents in 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):
a. Diode D1 fails open:
b. Diode D1 fails shorted:
c. Resistor R1 fails open:
d. Solder bridge (short) past resistor R1:
For each of these conditions, explain why the resulting effects will occur.
23. Predict how all component voltages and currents in 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):
a. Diode D1 fails open:
b. Diode D2 fails open:
c. Load resistor fails open:
d. Transformer T1 primary winding fails open:
For each of these conditions, explain why the resulting effects will occur.
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DT002
Industrial Electronics
Review Questions - I
24. An important parameter for many semiconductor components is thermal
resistance, usually specified in units of degrees Celsius per Watt. What does
this rating mean, and how is it related to temperature?
25. Rectifying diodes, like many other types of semiconductor components,
should be derated at elevated ambient temperatures. Datasheets often provide
"derating curves" that prescribe the maximum current for a range of ambient
temperatures. Explain just what "derating" is, and why it is so important for
semiconductor devices.
26. Trace the flow of all currents in this half of the AC cycle (note the polarity
symbols near the transformer's primary winding terminals):
Also, determine the polarity of DC voltage across the load resistor.
27. Now, trace the flow of all currents in the other half of the AC cycle (note the
polarity symbols near the transformer's primary winding terminals):
Also, determine the polarity of DC voltage across the load resistor.
28. In this rectifier circuit, the output voltage is less than half of the secondary
winding's rated voltage (12 volts). Why is this?
Also, determine whether this is a half-wave or a full-wave rectifier circuit, and
explain your answer.
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DT002
Industrial Electronics
Review Questions - I
29. A very common form of full-wave rectifier circuit is the bridge rectifier.
Typically, it is drawn as a "diamond" of four diodes:
Draw the connections in this illustration to form a bridge rectifier circuit,
receiving power from the transformer and delivering power to the light bulb:
30. Trace the current through this rectifier circuit at a moment in time when the
AC source's polarity is positive on right and negative on left as shown:
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DT002
Industrial Electronics
Review Questions - I
Also, mark the polarity of the voltage drop across Rload.
31. Trace the current through this rectifier circuit at a moment in time when the
AC source's polarity is positive on left and negative on right as shown:
Also, mark the polarity of the voltage drop across Rload.
32. Although not a popular design, some power supply circuits are
transformerless. Direct rectification of AC line power is a viable option in
some applications:
However, this form of AC-to-DC power conversion has some significant
limits. Explain why most power supply circuits utilize a transformer instead of
directly rectifying the line power as this circuit does.
33. An essential part of an AC-DC power supply circuit is the filter, used to
separate the residual AC (called the "ripple" voltage) from the DC voltage
prior to output. Here are two simple AC-DC power supply circuits, one
without a filter and one with:
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DT002
Industrial Electronics
Review Questions - I
Draw the respective output voltage waveforms of these two power supply
circuits (Vunfiltered versus Vfiltered).
34. Observe the following two waveforms, as represented on an oscilloscope
display measuring output voltage of a filtered power supply:
If both of these waveforms were measured on the same power supply circuit,
at different times, determine which waveform was measured during a period
of heavier "loading" (a "heavier" load being defined as a load drawing greater
current).
35. What does it mean if a power supply has a DC output with 5% ripple?
36. What parameters determine the frequency of a power supply's ripple voltage?
37. The ripple frequency of a half-wave rectifier circuit powered by 50 Hz AC is
measured to be 50 Hz. The ripple frequency of a full-wave rectifier circuit
powered by the exact same 50 Hz AC line voltage is measured to be 100 Hz.
Explain why the ripple frequency of the full-wave rectifier is twice that of the
half-wave rectifier.
38. Calculate the approximate DC output voltage of this power supply when it is
not loaded:
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DT002
Industrial Electronics
Review Questions - I
39. A simple AC-DC power supply circuit outputs about 6.1 volts DC without a
filter capacitor connected, and about 9.3 volts DC with a filter capacitor
connected:
Explain why this is. How can the addition of nothing but a capacitor have such
a great effect on the amount of DC voltage output by the circuit?
40. What does it mean if a power supply exhibits 2% voltage regulation?
41. Suppose you suspected a failed-open diode in this power supply circuit.
Describe how you could detect its presence without using an oscilloscope:
42. Predict how all component voltages and currents in 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):
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DT002
Industrial Electronics
Review Questions - I
a. Any one diode fails open:
b. Transformer secondary winding fails open:
c. Inductor L1 fails open:
d. Capacitor C1 fails shorted:
For each of these conditions, explain why the resulting effects will occur.
43. A technician is troubleshooting a power supply circuit that outputs
substantially less DC voltage than it should. The output voltage is supposed to
be 15 volts DC, but instead it is actually outputting less than 8 volts DC:
The technician measures approximately 18 volts AC (RMS) across the
secondary winding of the transformer. Based on this voltage measurement and
the knowledge that there is reduced DC output voltage, identify two possible
faults that could account for the problem and all measured values in this
circuit, and also identify two circuit elements that could not possibly be to
blame (i.e. two things that you know must be functioning properly, no matter
what else may be faulted). The circuit elements you identify as either possibly
faulted or properly functioning can be wires, traces, and connections as well as
components. Be as specific as you can in your answers, identifying both the
circuit element and the type of fault.
a. Circuit elements that are possibly faulted
i.
ii.
b. Circuit elements that must be functioning properly
i.
ii.
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