Zener diode (Zener Diod)
Principle A: It works in the reverse breakdown state of the voltage, when the reverse voltage reaches and exceeds the stable voltage, the reverse current suddenly increases, and the voltage across the diode is constant
Category B:
From high to low voltage regulation: low voltage regulator diode (
High voltage regulator diode (> 200V)
From the material: N type; P type
C. Main parameters
① Stable voltage VZ: the corresponding reverse working voltage under the specified voltage regulator tube and reverse working current IZ.
② Stable current IE
③ Dynamic resistance rZ;
④Maximum power dissipation PZM
⑤Maximum stable working current IZmax and minimum stable working current IZmin
⑥Temperature coefficient at, the higher the temperature, the greater the voltage regulation error
D. Use
① Clamp protection of drain and source
Silicon regulator diode regulator circuit
It uses the reverse breakdown characteristic of the Zener diode to stabilize the voltage. Due to the steep reverse characteristic and the large current change, it will only cause a small voltage change.
TVS is short for TVS
1. Features:
Under the specified reverse application conditions, when subjected to a high-energy transient overvoltage pulse, its working impedance can be immediately reduced to a very low conduction value, allowing large currents to pass and clamping the voltage to a predetermined level, which is effective Ground to protect precision components in electronic circuits from damage.
Fast reflection speed (pS level), small size, low clamping voltage, high reliability. Bidirectional TVS is suitable for AC circuits, and unidirectional TVS is generally used for DC circuits.
2. Classification:
Divided into two types of unipolar and bipolar according to polarity
3. Symbol: Symbol
4. 例 diagram and unidirectional protection diagram of the transient voltage suppression of the diode
5. Method of detecting diode
Use a multimeter R × 1k block to measure the quality of the tube
①For unipolar TVS, according to the method of measuring ordinary diodes, the forward and reverse resistance can be measured. Generally, the forward resistance is about 4k5, and the reverse resistance is infinite.
② For a bidirectional pole-type TVS, the red and black test leads can be exchanged arbitrarily to measure the resistance value between the two pins should be infinite, otherwise, it is declared that the pipe function is poor or damaged.
6. Examples of AC circuit applications:
The DC line uses unidirectional transient voltage suppression diodes, and the AC must use bidirectional transient voltage suppression diodes.
AC is the grid voltage, the transient voltage generated here is random, and sometimes lightning strikes (transient voltage generated by lightning induction) are also encountered, so it is difficult to quantitatively estimate the instantaneous pulse power PPR. But the maximum reverse working voltage must be selected correctly.
The general principle is to multiply the AC voltage by 1.4 times to select the maximum reverse working voltage of the TVS tube. The DC voltage is selected as 1.1 ~ 1.2 times to select the maximum reverse working voltage VRWM of the TVS tube. The following figure shows the schematic diagram of a microcomputer power supply using TVS for line protection
1. Add TVS tube at the incoming 220VAC to suppress the peak interference in the 220V AC power grid.
2. Add an interference filter to the transformer inlet to filter out small spikes.
3. Add TVS tube to the output terminal of the transformer at VAC = 20V to suppress the interference again.
4. When the DC 10V output is reached, the TVS tube is added to suppress the interference.
