Chapter 2
A certain power-supply filter produces an output with a ripple of 100mV peak-to-peak and a dc value of 20V. The ripple factor is
0.005
A 10V peak-to-peak sinusoidal voltage is applied across a silicon diode and series resistor. The maximum voltage across the diode is
0.7V
In a rectifier circuit, if the secondary winding in the transformer opens, the output is
0V
The peak value of the input to a half-wave rectifier is 10V. The diode must be able to withstand a reverse voltage of
10V
When a 60Hz sinusoidal voltage is applied to the input of a full-wave rectifier, the output frequency is
120Hz
In a certain positive clamper circuit, a 120V rms sine wave is applied to the input. The dc value of the output is
169V
When a diode is forward-biased and the bias voltage is increased, the voltage across the diode (Assuming complete model) will A) Increase B) Decrease C) Not change
A. Because of the small dynamic resistance, the graph has a small slope instead of a slope of 0
When a diode is reverse-biased and the bias voltage is increased, the reverse current (Assuming complete model) will A) Increase B) Decrease C) Not change
A. Because of the small dynamic resistance, the graph has a small slope instead of a slope of 0
When a diode is forward-biased and the bias voltage is increased, the forward current will A) Increase B) Decrease C) Not change
A. Because the bias voltage increased, the current slightly increases as well
If the barrier potential of a diode is exceeded, the forward current will A) Increase B) Decrease C) Not change
A. Once the barrier potential, 0.7V, is reached, the forward current will continue to increase.
Rectifier
An electronic circuit that converts ac into pulsating dc; one part of a power supply
Regulator
An electronic device or circuit that maintains an essentially constant output voltage for a range of input voltage or load values; one part of a power supply
If the bias voltage in Figure 2-55 is decreased, the positive portion of the output voltage will A) Increase B) Decrease C) Not change
B
If the turns ratio of the transformer in Figure 2-28 is decreased, the forward current through the diode will A) Increase B) Decrease C) Not change
B
If the value of the 3rd resistor in Figure 2-61 is decreased, the positive output voltage will A) Increase B) Decrease C) Not change
B. If the 3rd resistor decreases, so does the bias voltage. And when the bias voltage decreases, the output voltage does as well
T/F: When reverse biased, a diode ideally appears as a short.
False. It appears as it is open
T/F: The two regions of a diode are the anode and the collector.
False. It is the anode and the cathode
T/F: Line and load regulation are the same.
False. Line regulation is defined as the change in the output voltage of the regulator for a given change in input voltage. Load regulation is defined as the change in output voltage of a regulator over a certain range of load current values, that is from no load to full load
T/F: PIV stands for positive inverse voltage.
False. PIV stands for Peak Inverse Voltage
T/F: The output frequency of a half-wave rectifier is twice the input frequency
False. The output frequency is the same as the input frequency
T/F: The purpose of a clamper is to remove a dc level from a waveform
False. The purpose of a clamper is to add a dc level to an ac voltage using a diode and a capacitor
T/F: The purpose of the capacitor filter in the rectifier is to convert ac to dc
False. The purpose of the capacitor filter in a rectifier is used to eliminate the fluctuations in rectified output signal and produce a smooth constant-level dc voltage. The rectifier is the one that converts the ac input voltage to a pulsating dc voltage.
T/F: A smaller filter capacitor reduces the ripple.
False. The ripple factor can be reduced by increasing the value of the filter capacitor.
Filter
In a power supply, the capacitor used to reduce variation of the output voltage from a rectifier
When a silicone diode is open, a DMM will generally indicate
OL
Load regulation is determined by
changes in load current and output voltage
Line regulation is determined by
changes in output voltage and input voltage
When forward-biased, a diode
conducts current
Ideally, a diode can be represented by a
switch
The V-I curve for a diode shows
the amount of current for a given bias voltage
The ideal dc output voltage of a capacitor
the average value of the rectified voltage
A diode is normally operated in
the forward-bias region or the reverse-bias region
When the peak output voltage is 100V, the PIV for each diode in a center-tapped full-wave rectifier is (neglecting the diode drop)
200V
The input of a voltage doubler is 120V rms. The dc output is approximately
240V
When the rms output voltage of a bridge full-wave rectifier is 20V, the peak inverse voltage across the diodes is (neglecting the diode drop)
28.3V
If the input voltage to a voltage tripler has an rms value of 12V, the dc output voltage is approximately
36V
The average value of a full-wave rectified voltage with a peak value of 75V is
47.8V
In a certain biased limiter, the bias voltage is 5V and the input is 10V peak sine wave. If the positive terminal of the bias voltage is connected to the cathode of the diode, the maximum voltage at the anode is
5.7V
A 60V peak full-wave rectified voltage is applied to a capacitor-input filter. If f=120Hz, Rl=10k ohms, and C=10 micro-Faraday, the ripple voltage is
5V
When a 60Hz sinusoidal voltage is applied to the input of a half-wave rectifier, the output frequency is
60Hz
The total secondary voltage in a center-tapped full-wave rectifier is 125 V rms. Neglecting the diode drop the rms output voltage is
62.5
The average value of a half-wave rectified voltage with a peak value of 200V is
63.7V
The peak value of the input to a half-wave rectifier is 10V. The approximate peak value of the output is
9.3V
If the capacitor value in Figure 2-48 is decreased, the output ripple voltage will A) Increase B) Decrease C) Not change
A
If the input voltage in Figure 2-28 is increased, the peak inverse voltage across the diode will A) Increase B) Decrease C) Not change
A
If the input voltage in Figure 2-65 is increased, the peak negative value of the output voltage will A) Increase B) Decrease C) Not change
A
If the value of the 10k resistor in Figure 2-41 is decreased, the current through each diode will A) Increase B) Decrease C) Not change
A
Clamper
A circuit that adds a dc level to an ac voltage using a diode and a capacitor
Half-wave Rectfier
A circuit that converts an ac sinusoidal input voltage into a pulsating dc voltage with one output pulse occurring for each input cycle.
Full Wave Rectifier
A circuit that converts an ac sinusoidal input voltage into a pulsating dc voltage with two output pulses occurring for each input cycle.
The term bias means
A dc voltage is applied to control the operation of the device
Limiter
A diode circuit that clips off or removes part of a waveform above and/or below a specified level
Diode
A semiconductor device with a single pn junction that conducts current in only one direction
If the forward current in a diode is decreased, the diode voltage (Assuming complete model) will A) Increase B) Decrease C) Not change
B. If the forward current is decreasing, that means the biased voltage is decreasing. Because the diode voltage equals the biased voltage when less than 0.7, the correct answer is decreasing
If one of the diodes in Figure 2-41 opens, the average voltage to the load will A) Increase B) Decrease C) Not change
B. The average voltage to the load will decrease as there is no path for the current to flow through the load resistor
If the line voltage in Figure 2-51 is increased, ideally the +5V output will A) Increase B) Decrease C) Not change
C. A voltage regulator maintains a constant output voltage or current despite changes in the load current or the temperature, therefore, the output voltage doesn't change
When a diode is reverse-biased and the bias voltage is increased, the reverse current (Assuming practical model) will A) Increase B) Decrease C) Not change
C. Because the bias voltage was increased, the reverse current remains 0
When a diode is forward-biased and the bias voltage is increased, the voltage across the diode (Assuming practical model) will A) Increase B) Decrease C) Not change
C. Because the bias voltage was increased, the voltage across the diode remains at 0.7V
If the bias voltage in Figure 2-55 is increased, the negative portion of the output voltage will A) Increase B) Decrease C) Not change
C. Because the negative portion remains the same sinusoidal wave
If the PIV rating of the diodes in Figure 2-36 is increased, the current through the 10k resistor will A) Increase B) Decrease C) Not change
C. The PIV rating of the diode is dependent on the output voltage and the output voltage is independent of the PIV rating of the diodes. So increasing the PIV rating does not affect the current through the load resistor
If the frequency of the input voltage in Figure 2-36 is increased, the output voltage will A) Increase B) Decrease C) Not change
C. The change in frequency of the input voltage does no affect anything in the circuit
If the forward current in a diode is increase, the diode voltage (Assuming practical model) will A) Increase B) Decrease C) Not change
C. The diode voltage remains 0.7V
Bias
The application of a dc voltage to a diode to make it either conduct or block current
In a practical diode model
The barrier potential is taken into account
In the complete diode model,
The barrier potential, the forward dynamic resistance, and the reverse resistance is all taken into account
Load Regulation
The change in output voltage of a regulator for a given range of load currents, normally expressed as a percentage
Line Regulation
The change in the output voltage of the regulator for a given change in input voltage, normally expressed as a percentage
Forward Bias
The condition in which a diode conducts current
Reverse Bias
The condition in which a diode prevents current
When a diode is forward-biased
The current is produced by both holes and electrons
Peak Inverse Voltage (PIV)
The maximum value of a reverse voltage across a diode that occurs at the peak of the input cycle when the diode is reverse-biased
Ripple Voltage
The small variation in the dc output voltage of a filtered rectifier cause by the charging and discharging of the filter capacitor
T/F: A basic half-wave rectifier consists of one diode
True
T/F: A bridge rectifier uses four diodes
True
T/F: A diode can conduct current in two directions with equal ease.
True
T/F: A diode conducts current when forward-biased
True
T/F: A diode limiter is also known as a clipper
True
T/F: Each diode in a full-wave rectifier conducts for the entire input cycle.
True
T/F: In a bridge rectifier, two diodes conduct during each half-cycle of the input
True
T/F: The diode in a half-wave rectifier conducts for the entire input cycle
True
T/F: The output frequency of a full-wave rectifier is twice the input frequency
True
T/F: The output voltage of a filtered rectifier always has some ripple voltage.
True
T/F: Two types of current in a diode are electron and hole
True
T/F: Voltage multipliers use diodes and capacitors.
True
If one of the diodes in a bridge full-wave rectifier opens, the output is
a half-wave rectified voltage
To forward-bias a diode
an external voltage is applied that is positive to the anode and negative at the cathode an external voltage is applied that is positive at the p region and negative at the n region
When a silicone diode is working properly in forward boas, a DMM in the diode test position will indicate
approximately 0.7V
The dynamic resistance can be important when a diode is
forward-biased
If the load resistance of a capacitor-filtered full--wave rectifier is reduced, the ripple voltage
increases
For a silicon diode, the value of the forward-bias voltage typically
must be greater than 0.7V
although current is blocked in reverse bias
there is a very small current due to minority carriers
If you are checking a 60Hz full-wave bridge rectifier and observe that the output has a 60Hz ripple,
there is an open diode