What is the function and working principle of transient suppression diodes?

What is the function and working principle of transient suppression diodes?

The function of transient suppression diodes:

(1) Adding TVS diodes to the signal and power lines can prevent the failure of microprocessors or microcontrollers due to transient surges, such as electrostatic discharge effects, AC power surges, and switching power supply noise.

(2) The electrostatic discharge effect can release pulses exceeding 10000V and 60A, and can last for 10ms; However, general TTL devices may be damaged when encountering 10V pulses exceeding 30ms. The use of TVS diodes can 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.

The working principle of transient suppression diode:

The device is connected in parallel with the circuit. When the circuit works normally, it is in the cut-off state (High impedance), which does not affect the normal operation of the line. When the circuit has an abnormal overvoltage and reaches its breakdown voltage, it quickly changes from the High impedance to the low resistance state, providing a low impedance conduction path for the instantaneous current, while clamping the abnormal high voltage within a safety level, so as to protect the protected IC or line; When the abnormal overvoltage disappears, it returns to the high resistance state and the circuit works normally.

Transient suppression diode selection:

① When using TVS diodes, they are generally connected in parallel to the protected circuit. In order to limit the current flowing through the TVS diode to not exceed the peak current IPP allowed by the diode, current limiting elements such as resistors, self recovery fuses, inductors, etc. should be connected in series on the line.

② Selection of breakdown voltage VBR: The breakdown voltage of TVS diodes should be selected based on the highest working voltage UM of the line according to the formula: VBRmin ≥ 1.2 UM or VRWM ≥ 1.1 UM. Communication: UM=1.414Uac, for example, for 220V AC, UM=1.414 * 220=311 (V); DC: UM=Udc