Application and Analysis of TVS Diode

Application and analysis of TVS diode
Transient voltage suppressor (TVS) has the advantages of fast response time, large transient power, low leakage current, small breakdown voltage deviation, easy control of clamping voltage, no damage limit, and small size. At present, it has been widely used in various fields such as computer systems, communication equipment, AC/DC power supplies, automobiles, household appliances, and instruments. This article will combine the characteristics of TVS application and precautions for use, introduce several typical application circuits of TVS, and discuss in detail how to apply TVS correctly and make TVS The application performance is the best.
In actual application circuits, the best way to deal with damage to devices caused by transient pulses is to divert the transient current away from sensitive devices. To achieve this purpose, connect the TVS in parallel with the protected line on the circuit board. In this way, when the instantaneous voltage exceeds the normal working voltage of the circuit, the TNS will undergo an avalanche breakdown, thereby providing an ultra-low impedance path for the instantaneous current. As a result, the instantaneous current is drawn away through the TVS, thereby avoiding the protected device, and Keep the protected circuit at cut-off voltage until the voltage returns to normal value. After that, when the instantaneous pulse is over, the TVS diode will automatically return to the high-impedance state, and the whole circuit will enter the normal voltage state.

1 Three major characteristics of TVS application
1) Adding TVS diodes to signal and power lines can prevent microprocessors or single-chip microcomputers from being damaged by instantaneous pulses, such as electrostatic discharge effects, AC power surges, and switching power supply noises. out of order.
2) The electrostatic discharge effect can release pulses exceeding 10000V and 60A, and can last for 10ms; while general TTL devices, when encountering 10V pulses exceeding 30ms, will lead to damage. The use of TVS diodes can effectively absorb pulses that will damage devices and eliminate interference (Crosstalk) caused by switching between buses.
3) Placing the TVS diode between the signal line and the ground can prevent the data and control bus from being affected by unnecessary noise.

2 Matters needing attention in the use of TVS tube
The relationship between the absorbed power (peak value) of the transient voltage and the pulse width of the transient voltage. The manual only gives the absorbed power (peak value) at a specific pulse width, but the pulse width in the actual line is unpredictable, so it must be estimated in advance. The wide pulse should be used with derating.
For the protection of small current loads, a current-limiting resistor can be consciously added to the line. As long as the resistance of the current-limiting resistor is appropriate, it will not affect the normal operation of the line, but the current generated by the current-limiting resistor to the interference will be greatly reduced. . This makes it possible to choose a TVS tube with a smaller peak power to protect the small current load line.
For the suppression of repeated transient voltages, it is especially worth noting whether the steady-state average power of the TVS tube is within the safe range.