What is the role of the power tube?

Last Update Time: 2018-12-01 11:43:01

The role of the Zener in the switching power supply:

1, the reference voltage source

The circuit of the reference voltage source is provided by the Zener diode DZ, and the DC voltage is obtained by full-wave rectification and capacitance filtering, and then the voltage regulator circuit composed of the resistor R and the Zener diode DZ provides a relatively stable load to the load RL. DC voltage. When the AC power supply voltage is unstable or the load changes, such as an increase in the AC voltage, the output voltage Uo rises and the load voltage UL increases. The voltage applied across the Zener diode DZ increases accordingly. Assuming that the Zener diode is in a breakdown state at this time, the volt-ampere characteristics of the Zener diode are known. The voltage of the Zener diode increases slightly, the current of it increases sharply, the current flowing through the resistor R increases, and the UZ voltage increases, so that the output voltage cannot rise. Thereby maintaining the output voltage substantially unchanged. This is the basic principle of using a Zener diode as the reference power supply.

2. Overvoltage protection circuit

The overvoltage protection circuit is divided into an overvoltage protection and an overvoltage protection circuit.

Some circuits and devices are not allowed to operate for longer periods of time at low voltages. For this reason, Zener diodes can be used as low voltage protection circuits. When the power supply voltage US exceeds the breakdown voltage of the Zener diode, the Zener diode DZ breaks through and there is enough current to excite the relay, and the contact J1 acts to supply the load RL. Once the power supply voltage is too low (not reaching the steady voltage value of the Zener diode), no current flows through the relay J, and J1 disconnects the load and is separated from the power supply. The selection principle of the current limiting resistor SR is: SR=SU/Ij-Rj

Where Us is the power supply voltage, Ij is the relay operating current. Rj is the relay DC resistance.

Excessive voltage protection circuit: The surge voltage from the power supply is too high. It can be protected by a Zener tube.Under normal conditions, the power supply voltage is lower than the breakdown voltage of the Zener diode, and the reverse resistance of the voltage regulator tube is large. The power supply is equivalent to an open circuit, and the voltage regulator tube is not conductive. When the power supply voltage is too high, the Zener diode is broken through and the current is increased, and the voltage is limited.

3. Limiting effect

In order to prevent the output voltage of the amplifier from exceeding the limit value, a voltage limiting tube limiting circuit can be used. The output voltage peak is limited to approximately equal to the regulated voltage of the Zener diode

The circuit is an op amp limiter circuit, and DZ1 and DZ2 are docked in the feedback circuit. In normal operation, the output voltage is less than the stable voltage of the Zener diode DZ, and this feedback branch does not work. However, when the input voltage reaches the condition, a Zener tube is broken down. The other is forward-passed, and the negative feedback is boosted to limit the output voltage to a range.

 

This article is from ALLICDATA ELECTRONICS LIMITED.