What is a transient voltage suppressor?

Transient Voltage Suppressor (Transient Voltage Suppressor) is abbreviated as TVS and is a high-efficiency protection device in the form of a diode. Some literatures are also TVP, AJTVS, SAJTVS, and so on. When the two poles of the TVS diode are subjected to reverse transient high-energy shock, it can change the high impedance between its two poles to low impedance at the speed of the order of 10-12 seconds, absorbing up to several kilowatts of surge power, making the two poles The voltage clamp is located at a predetermined value to effectively protect the precision components in the electronic circuit from damage caused by various surge pulses. Due to its advantages of fast response time, large transient power, low leakage current, small breakdown voltage deviation, easy to control clamping voltage, no damage limit, and small size, it has been widely used in computer systems, communication equipment, and power supplies. , household appliances and other fields. Specifically there are the following three characteristics:

1. Adding TVS diodes to the signal and power lines can prevent microprocessors or microcontrollers from malfunctioning due to momentary surges such as electrostatic discharge effects, surges in AC power sources, and noise from switching power supplies.

2. The electrostatic discharge can release more than 10000V and 60A pulses, and can last for 10ms. In general, TTL devices that encounter more than 30ms 10V pulse will lead to damage. With TVS diodes, pulses that can cause damage to the device can be effectively absorbed and crosstalk caused by switching between buses can be eliminated.

3. Place the TVS diode between the signal line and ground to avoid unnecessary noise impact on the data and control bus.

TVS characteristics and main parameters 1. TVS characteristics The TVS circuit symbols are the same as those of ordinary zener diodes. Its forward characteristic is the same as a normal diode; its reverse characteristic is a typical PN junction avalanche device. Under the transient peak pulse current, when the current flowing through the TVS rises from the original reverse leakage ID to IR, the voltage appearing at the two poles rises from the rated reverse turn-off voltage VWM to the breakdown voltage VBR. The TVS is breakdown. With the occurrence of the peak pulse current, the current flowing through the TVS reaches the peak pulse current IPP. The voltage at its two poles is clamped below the predetermined maximum clamp voltage. Afterwards, as the pulse current decays exponentially, the voltage at the two poles of the TVS continues to drop and eventually returns to the initial state. This is where TVS suppresses the surge power that may occur and protects the electronic components.

2. Characteristics of TVS Parameter 1 Maximum Reverse Leakage Current ID and Rated Reverse Shutdown Voltage VWM: VWM is the maximum continuous operating DC or pulse voltage of TVS. When this reverse voltage is added between the two poles of TVS, it is in reverse. In the off state, the current flowing through it should be less than or equal to its maximum reverse leakage current ID.

2 Minimum breakdown voltage VBR and breakdown current IR: VBR is the minimum avalanche voltage of TVS. At 25°C, TVS is not conducting before this voltage. When the TVS flows through the specified 1mA current (IR), the voltage between the two poles of the TVS is added to the minimum breakdown voltage VBR. According to the TVS VBR and the standard value of the degree of dispersion, TVS can be divided into ± 5% VBR and peaceful coexistence ± 10% VBR. VWM=0.85VBR for ±5% VBR; VWM=0.81 VBR for ±10% VBR.

3 Maximum clamp voltage VC and maximum peak pulse current IPP: When the pulse peak current IPP with a duration of 20 microseconds flows through TVS, the maximum peak voltage appearing across its two poles is VC. It is a combination of both the series resistance and the voltage rise due to the temperature coefficient. VC and IPP reflect the surge suppression capability of TVS devices. The ratio of VC to VBR is called the clamping factor and is generally between 1.2~1.4.

4 Capacitance C Capacitance: C is measured at the specific 1 MHz frequency determined by the avalanche section of the TVS. The size of C is proportional to the current carrying capacity of the TVS. Excessive C will attenuate the signal. Therefore, C is an important parameter for selecting TVS for data interface circuits.

5 Maximum peak pulse power consumption PM PM is the maximum peak pulse dissipation power that the TVS can withstand. For the specified test pulse waveforms and PM values ​​for various TVSs, please refer to the relevant product manual. At a given maximum clamp voltage, the greater the power dissipation, PM, the greater its inrush current withstand capability; the lower the clamp voltage, VC, at a given power consumption, the lower the inrush current withstand capability. Big. In addition, the peak pulse power consumption is also related to the pulse shape, duration, and ambient temperature. Moreover, the transient pulses that TVS can withstand are non-repetitive, and the device-defined pulse repetition frequency (ratio between duration and rest time) is 0.01%. If there are repetitive pulses in the circuit, the “accumulation” of pulse power should be considered. It may damage the TVS.

6 Clamping time TC:TC is the time from zero to the minimum breakdown voltage VBR. For unipolar TVS less than 1 x 10-12 seconds; for bipolar TVS less than 1 x 10-11 seconds.