What is a transient suppression diode?

Characteristics of transient suppression diode - Transient suppression diode parameters

What is a transient suppression diode

Transient Voltage Suppressor (TVS), abbreviated as TVS, is a high-performance protective device in the form of a diode. When the two poles of a TVS diode are subjected to a reverse transient high-energy impact, it can transform the high impedance between its two poles into low impedance at a speed of 10 ^ -12 seconds, absorbing surge power of up to several kilowatts, and clamping the voltage between the two poles at a predetermined value, effectively protecting precision components in electronic circuits from damage caused by various surge pulses.

Characteristics of transient suppression diode

1. Adding TVS diodes to the signal and power lines can prevent the failure of microprocessors or microcontrollers caused by momentary pulses such as electrostatic discharge effects, AC power surges, and noise from switching power supplies.

2. The electrostatic discharge effect can release pulses exceeding 10000V and 60A, and can last for 10ms; However, typical TTL devices will be damaged when exposed to 10V pulses exceeding 30ms. By using TVS diodes, it is possible to effectively absorb pulses that can cause device damage and eliminate interference caused by switches between buses (Crosstalk).

3. Placing the TVS diode between the signal line and ground can prevent unnecessary noise from affecting the data and control bus.

Transient suppression diode parameters

① Maximum reverse leakage current ID and rated reverse turn off voltage VWM.

VWM is the maximum continuous DC or pulse voltage of TVS. When this reverse voltage is applied between the two poles of TVS, it is in a reverse off state, and 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 for TVS. At 25 ℃, TVS is non-conductive before this voltage. When a specified 1mA current (IR) flows through the TVS, the voltage added between the two poles of the TVS is its minimum breakdown voltage VBR. According to the degree of dispersion between the VBR of TVS and the standard value, TVS can be divided into two types: ± 5% VBR and ± 10% VBR. For ± 5% VBR, VWM=0.85VBR； For ± 10% VBR, VWM=0.81VBR。

③ Maximum clamping voltage VC and maximum peak pulse current IPP

When a pulse peak current IPP with a duration of 20 microseconds flows through the TVS, the maximum peak voltage that appears between its two poles is VC. It is a combination of voltage rise on a series resistor and due to temperature coefficient. VC and IPP reflect the surge suppression capability of TVS devices. The ratio of VC to VBR is called the clamping factor, which is generally between 1.2 and 1.4.

④ Capacity C

The capacitance C is determined by the TVS avalanche junction cross-section and measured at a specific frequency of 1MHz. The size of C is directly proportional to the current carrying capacity of TVS, and if C is too large, it will cause signal attenuation. Therefore, C is an important parameter for selecting TVS in data interface circuits.

⑤ Maximum peak pulse power consumption PM

PM is the maximum peak pulse dissipation power that TVS can withstand. Please refer to the relevant product manual for the prescribed test pulse waveform and various TVS PM values. At a given maximum clamping voltage, the greater the power consumption PM, the greater its ability to withstand surge currents; At a given power consumption PM, the lower the clamping voltage VC, the greater its ability to withstand surge currents. In addition, peak pulse power consumption is also related to pulse waveform, duration, and ambient temperature. Moreover, the transient pulses that TVS can withstand are non repetitive, and the device's specified pulse repetition frequency (the ratio of duration to interval time) is 0.01%. If repetitive pulses occur in the circuit, the "accumulation" of pulse power should be considered, which may damage the TVS.

⑥ Clamping time TC

TC is the time for the voltage at both ends of TVS to go from zero to the minimum breakdown voltage VBR. For unipolar TVS, it is generally 1 × 10-12 seconds; For bipolar TVS, it is generally 1 × 10-11 seconds.