85 Questions
Which two types of reverse breakdown can occur in a zener diode?
Avalanche and zener breakdown
Which type of breakdown occurs in zener diodes at low reverse voltages?
Zener breakdown
What is the general operating region for zener diodes called?
Reverse-breakdown region
What happens to the zener impedance as the reverse current increases?
It decreases
What is the key feature of a zener diode in breakdown?
It acts as a voltage regulator
Which of the following is the symbol for a zener diode?
A letter Z
True or False: A zener diode is designed for operation in the forward-bias region.
False
What is the key characteristic of zener diode operation?
Constant voltage
What is the purpose of a zener diode in a power supply?
To provide a stable reference voltage
What is zener breakdown?
A type of avalanche breakdown
Zener diodes can be used as voltage regulators because they maintain a nearly constant output voltage across their terminals. However, their efficiency is limited, so they are best suited for applications that require low current to the load.
True
The zener voltage of a 1N4736A diode is 6.8V at a test current of 37mA. What is the voltage across the zener terminals when the current is 50mA?
6.85V
In what region of their characteristic curve are zener diodes operated?
Reverse bias
At what value of zener current is the zener voltage normally specified?
Test current
What does a positive temperature coefficient of 0.05%/°C mean?
The zener voltage increases by 0.05% for every degree Celsius increase in temperature.
According to the datasheet, how can the maximum current be calculated from the power specification of 1 W?
The maximum current is calculated by dividing the power specification by the voltage.
What does IZM represent in the context of the datasheet?
The maximum value of the current.
What does IZK represent in the context of the datasheet?
The minimum value of the current.
What happens to the output voltage when the input voltage increases?
The output voltage remains nearly constant.
What happens to the output voltage when the input voltage decreases?
The output voltage remains nearly constant.
Which temperature is used to measure the zener voltage on the datasheet?
30°C
What is the maximum power dissipation of the zener diode at 50°C?
272 mW
What is the derating factor for the zener diode?
0.5 W/°C
What is the maximum power dissipation of the 1N4728A zener diode?
1.0 W
What is the zener voltage for the 1N4732A zener diode at a test current of 53 mA?
4.465 V
According to Ohm's law, what is the ratio of impedance, as expressed in the following equation?
¢ VZ to ¢ IZ
What is the best reason to avoid operating a zener diode near the knee of the curve?
The impedance changes dramatically in that area
What is the formula for calculating the zener impedance?
ZZ = ¢ VZ / ¢ IZ
What does the temperature coefficient specify?
The percent change in zener voltage for each degree Celsius change in temperature
What is the formula for calculating the change in zener voltage for a given junction temperature change?
¢ VZ = VZ * TC * ¢ T
True or false: Zener diodes are commonly used as voltage regulators for power supplies and instruments.
True
True or false: The zener diode maintains a nearly constant dc voltage under the proper operating conditions.
True
True or false: The breakdown voltage of a zener diode is set by controlling the doping level during manufacture.
True
True or false: When a zener diode reaches reverse breakdown, its voltage remains almost constant even though the current changes drastically.
True
True or false: Zener diodes are most efficient for applications that require high current to the load.
False
True or false: Zener breakdown occurs in zener diodes at low reverse voltages.
True
True or false: Zeners with breakdown voltages greater than approximately 5 V operate predominately in avalanche breakdown.
True
True or false: Zener diodes are designed to operate in forward breakdown.
False
True or false: The zener diode maintains a nearly constant voltage across its terminals for values of reverse current ranging from IZK to IZM.
True
True or false: The zener impedance decreases as the reverse current increases.
False
True or false: According to Ohm's law, the ratio of $\Delta V_Z$ to $\Delta I_Z$ is the impedance of a zener diode?
True
True or false: The zener impedance is calculated using the equation $ZZ = \frac{\Delta V_Z},{\Delta I_Z}$?
True
True or false: The zener impedance changes dramatically near the knee of the characteristic curve?
True
True or false: The zener voltage of a 1N4736A diode is 6.8V at a test current of 37mA?
False
True or false: A zener diode exhibits a certain change in $V_Z$ for a certain change in $I_Z$ on a portion of the linear characteristic curve?
True
True or False: The zener voltage for a 1N4728A can range from 3.315 V to 3.465 V with a typical value of 3.3 V at a test current of 76 mA.
True
True or False: The maximum zener impedance is the maximum zener impedance at the specified test current.
True
True or False: Reverse leakage current is specified for a reverse voltage that is less than the knee voltage.
True
True or False: The zener voltage for a 1N4736A zener diode is 6.8 V at a test current of 37 mA.
True
True or False: Zener diodes are operated in the breakdown region of their characteristic curve.
True
True or false: A zener diode can dissipate a maximum power of 400 mW at 25°C?
True
True or false: The derating factor for the zener diode is 0.5 W/°C?
True
True or false: The maximum power a zener diode can dissipate at a temperature of 75°C is 272 mW?
True
True or false: The maximum power a 50 W zener diode can dissipate at 160°C is 128 mW?
False
True or false: The zener voltage is measured with the device junction at a lead temperature of 30°C ± 1°C and a lead length of 3/8"?
True
True or False: The maximum current of a zener diode can be calculated from the power specification of 1W and the zener voltage.
False
True or False: The minimum and maximum values of a zener diode's current represent worst-case operation.
True
True or False: As the input voltage increases, the output voltage of a zener diode remains nearly constant.
True
True or False: As the input voltage decreases, the output voltage of a zener diode remains nearly constant.
True
True or False: Zener diodes can be used as voltage regulators because they maintain a nearly constant output voltage across their terminals.
True
What are the two types of reverse breakdown that can occur in a zener diode?
Avalanche and zener breakdown
What is the purpose of a zener diode in a power supply?
To regulate the voltage and maintain a nearly constant voltage across its terminals
What is the key characteristic of zener diode operation?
Maintaining a nearly constant voltage across its terminals over a specified range of reverse-current values
What is the zener voltage for the 1N4732A zener diode at a test current of 53 mA?
2.9 V
What is the maximum power dissipation of the 1N4728A zener diode?
1 W
What is the formula for calculating the maximum current of a zener diode?
$IZM = \frac{PD_{max}},{VZ}$
What is the formula for calculating the voltage across the resistor for the minimum zener current?
$V_R = V_{IN} - V_Z$
What is the formula for calculating the voltage across the zener terminals for a given current?
$V_Z = V_{IN} - I_Z \cdot R$
What is the purpose of a zener diode in a power supply?
To regulate the output voltage and provide voltage stabilization
What happens to the output voltage when the input voltage decreases?
The output voltage remains nearly constant
What is the equation for calculating the zener impedance?
$ZZ = \frac{\Delta VZ}{\Delta IZ}
What is the formula for calculating the change in zener voltage for a given junction temperature change?
$\Delta VZ = VZ \cdot TC \cdot \Delta T
What is the maximum power dissipation of the zener diode at 50°C?
$PD(derated) = PD(max) - \frac{mW}{°C} \cdot T
What is the key feature of a zener diode in breakdown?
The key feature of a zener diode in breakdown is its ability to maintain a nearly constant dc voltage across its terminals.
What does a positive temperature coefficient of 0.05%/°C mean?
A positive temperature coefficient of 0.05%/°C means that the zener voltage increases by 0.05% for every degree Celsius increase in temperature.
What is the symbol for a zener diode?
The symbol for a zener diode is shown in Figure 3–1.
What is the key characteristic of zener diode operation?
The key characteristic of zener diode operation is that its voltage remains almost constant even though the current changes drastically when it reaches reverse breakdown.
What is zener breakdown?
Zener breakdown is the phenomenon where a zener diode starts conducting current in the reverse direction when the reverse voltage across it exceeds its breakdown voltage.
What is the formula for calculating the change in zener voltage for a given junction temperature change?
The formula for calculating the change in zener voltage for a given junction temperature change is: $\Delta V_Z = V_Z \cdot \alpha \cdot \Delta T$, where $V_Z$ is the zener voltage, $\alpha$ is the temperature coefficient, and $\Delta T$ is the change in temperature.
What is the maximum power dissipation of the 1N4728A zener diode?
The maximum power dissipation of the 1N4728A zener diode is 1W.
What is the purpose of a zener diode in a power supply?
Zener diodes can be used as voltage regulators because they maintain a nearly constant output voltage across their terminals.
What is the maximum power dissipation of the 1N4728A zener diode?
The maximum power dissipation of the 1N4728A zener diode is 1W.
What is the zener voltage for the 1N4732A zener diode at a test current of 53 mA?
The zener voltage for the 1N4732A zener diode at a test current of 53 mA is 3.2 V.
What does a positive temperature coefficient of 0.05%/°C mean?
A positive temperature coefficient of 0.05%/°C means that the zener voltage increases by 0.05% for every degree Celsius increase in temperature.
What is the formula for calculating the change in zener voltage for a given junction temperature change?
The formula for calculating the change in zener voltage for a given junction temperature change is $\Delta V_Z = V_{Z0} \cdot \beta \cdot \Delta T_j$ where $\Delta V_Z$ is the change in zener voltage, $V_{Z0}$ is the initial zener voltage, $\beta$ is the temperature coefficient, and $\Delta T_j$ is the change in junction temperature.
Study Notes
Topic: Zener Diodes
Introduction
- A zener diode is a type of diode that can operate in reverse bias, allowing it to regulate voltage.
- Zener diodes are designed to operate in the reverse-breakdown region, which is not the case for ordinary diodes.
Characteristics of Zener Diodes
- Zener diodes are designed to operate in the reverse-breakdown region, which is characterized by a constant voltage across the terminals.
- The voltage at which breakdown occurs is known as the zener voltage (VZ).
- Zener diodes have a very low impedance when operating in the reverse-breakdown region.
- Zener diodes have a specific current range (IZK to IZM) within which they can operate reliably.
Zener Breakdown
- Two types of reverse breakdown occur in zener diodes: Zener breakdown and avalanche breakdown.
- Zener breakdown occurs at lower reverse voltages (typically < 5V) and is characterized by a very thin depletion region.
- Avalanche breakdown occurs at higher reverse voltages (typically > 5V) and is characterized by a thicker depletion region.
Temperature Coefficient
- The temperature coefficient (TC) specifies how much the zener voltage changes with temperature.
- A positive TC means the zener voltage increases with temperature, while a negative TC means the zener voltage decreases with temperature.
Power Dissipation
- The maximum power dissipation (PD(max)) of a zener diode is specified by the manufacturer.
- The power dissipation is typically derated above a certain temperature (e.g., 50°C).
Zener Regulation
- Zener diodes can be used to regulate voltage by maintaining a constant output voltage across the terminals.
- The output voltage is determined by the zener voltage (VZ).
- The input voltage can vary, but the output voltage remains relatively constant.
Limitations of Zener Regulation
- Zener regulators are not particularly efficient and are limited to low-current applications.
- The input voltage variation is limited by the minimum and maximum current values (IZK and IZM) with which the zener can operate.
Applications of Zener Diodes
- Zener diodes can be used as voltage references, regulators, and simple limiters or clippers.
- They are commonly used in power supplies, voltage regulators, and other electronic circuits.### The Zener Diode
Characteristics
- The zener diode is a type of voltage regulator that provides a stable reference voltage
- Operates in the reverse breakdown region
- Two types of reverse breakdown: zener and avalanche
- Zener breakdown occurs at low reverse voltages (< 5V), avalanche breakdown at higher reverse voltages (> 5V)
- Available with breakdown voltages from less than 1V to over 250V
Zener Diode Symbol and Operation
- Symbol: bent line resembling the letter Z
- Operates in reverse breakdown, maintaining a nearly constant voltage across its terminals
- Minimum current required to maintain regulation: IZK (knee current)
- Maximum current: IZM, above which the diode may be damaged
- Typical operating range: IZK < IZ < IZM
Zener Voltage Regulation
- Key feature: maintains a nearly constant voltage across its terminals over a specified range of reverse currents
- Ideal model: constant voltage drop
- Practical model: includes zener impedance (ZZ) which affects the voltage drop
Temperature Coefficient
- Specifies the percent change in zener voltage per degree Celsius change in temperature
- Positive temperature coefficient: zener voltage increases with temperature increase
- Negative temperature coefficient: zener voltage decreases with temperature increase
Power Dissipation and Derating
- Maximum power dissipation: PD(max), typically specified for a certain temperature
- Derating: maximum power dissipation is reduced at temperatures above the specified temperature
- Derating factor: expressed in mW/°C
Zener Diode Applications
- Voltage regulator: provides a stable reference voltage
- Regulator circuit: includes a series current-limiting resistor and a zener diode
- Regulation characteristics:
- Input voltage variation: output voltage remains nearly constant
- Load current variation: output voltage remains nearly constant
Zener Diode Datasheet
- Provides information on:
- Absolute maximum ratings
- Electrical characteristics (zener voltage, zener impedance, etc.)
- Operating and storage temperature range
This quiz tests your knowledge on zener diodes and their power dissipation capabilities at different temperatures. Can you determine the maximum power a zener diode can dissipate at various temperatures? Take the quiz to find out!
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