When the voltage regulator is connected in the reverse direction, when the reverse voltage is less than the breakdown voltage, the reverse current is very small and the dynamic resistance is very large. Generally, the larger the working current, the smaller the dynamic resistance and the better the voltage regulation performance. When the reverse voltage is greater than the breakdown voltage, the current flowing through the diode increases sharply, but the voltage across it remains basically unchanged. This can be used to stabilize the voltage. Applications of Zener diodes: 1. Surge protection circuit (as shown in Figure 2): The Zener diode breaks down at an accurate voltage, which makes it possible to use it as a limiting or protective element. Since Zener diodes of various voltages are available, they are particularly suitable for this application. The Zener diode D in the figure is used as an overvoltage protection device. As long as the power supply voltage VS exceeds the voltage regulation value of the diode, D will be turned on, causing the relay J to attract the load RL and separate it from the power supply.
2. Overvoltage protection circuit in the TV (as shown in Figure 3): EC is the main supply voltage of the TV. When the EC voltage is too high, D will be turned on, the transistor BG will be turned on, and its collector potential will change from the original high level (5V) to a low level, and the TV will enter the standby protection state through the control of the standby control line.
3. Arc suppression circuit is shown in Figure 4: If a suitable voltage-stabilizing diode is connected in parallel to the inductor (it can also be connected to an ordinary diode with the same principle), when the coil is cut off in the on state, the high voltage generated by the release of its electromagnetic energy is absorbed by the diode, so when the switch is turned off, the arc of the switch is eliminated. This application circuit is used more in industry, such as some high-power electromagnetic suction control circuits. 4. Series voltage-stabilizing circuit (as shown in Figure 5): In this circuit, the voltage-stabilizing diode is connected in series, and the base of BG is clamped at 13V by the voltage-stabilizing diode D, so its emitter outputs a constant 12V voltage. This circuit is used in many occasions.
5. In addition to making voltage-stabilizing circuits, voltage-stabilizing diodes can also be used as one-time protection circuits. For example, in important parts, it is forbidden to increase the voltage and damage the valuable components. You can use a voltage regulator tube to be connected in reverse parallel with the power supply at that place. When the power supply voltage suddenly increases due to a fault and exceeds the voltage regulation value of the voltage regulator tube, the voltage regulator tube quickly switches from the cut-off state to reverse breakdown, directly short-circuiting the power supply, burning the fuse or current limiting protection resistor, and protecting all loads of the power supply branch from damage due to overvoltage. Since this type of voltage regulator tube for protection is usually inactive, it can be temporarily used in emergency repairs. Experienced maintenance personnel can even use local materials in emergency situations and disassemble them for flexible use as scarce maintenance accessories.
For the power supply, this is a constant current circuit, for the voltage regulator, this is a common collector circuit, for the load, this is a common base circuit with Rc equal to zero!!
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Published on 2017-11-29 00:02
The real breakdown is the destruction of the structure, which is irreversible even if a current-limiting element is connected in series. Not all PN junctions can handle the Zener transition and avalanche transition. Otherwise, why would we invent the Zener diode? !
5. This is called an "electronic crowbar". It is faster to use a thyristor, but it is still much slower than a TVS (it turns on in 1 femtosecond!). 4. The voltage regulator is a voltage regulator tube, and the transistor is a current expansion tube. The current flowing from the voltage regulator tube to the load when the voltage regulator tube is connected in parallel with the load is used to control the current expansion degree of the transistor. 3. The voltage regulator tube in Figure 4 is just an ordinary diode connection. If you want to quickly demagnetize the relay, turn the voltage regulator tube upside down and change the resistor to an ordinary diode.
For the power supply, this is a constant current circuit, for the voltage regulator, this is a common collector circuit, and for the load, this is a common base circuit with Rc equal to zero! !
Details
Published on 2017-11-29 00:02
For the power supply, this is a constant current circuit, for the voltage regulator, this is a common collector circuit, for the load, this is a common base circuit with Rc equal to zero!!
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