The working principle of TVs transient suppression diode is the same as that of Zener diode, but there are differences in structure. The biggest difference is that the PN junction area composed of general zener diodes is very small, and it can withstand small reverse current.
Generally, the maximum reverse current of low-power Zener (0.5 ~ 1W) is tens of milliamps to hundreds of milliamps; The PN junction area of the transient suppression diode is large, the dissipated power is large, and the maximum reverse current can be up to several to tens of amps. Therefore, it can absorb the instantaneous large current caused by the instantaneous high voltage pulse. Generally, the zener diode is 0.5 ~ 3W, while the transient diode reaches 300W to 1500W, and some for high voltage can reach more than 10kW. For example, a transient diode with reverse breakdown voltage VBR of 6.4 ~ 7.3v and dissipation power of 500W can withstand a maximum pulse current IPP of 52 ~ 54a.
The circuit using transient diode as protection is shown in the figure below, which is connected in parallel to the protection circuit. Note that it does not require a current limiting resistor R. If the working voltage of the protected circuit is + 5V, a diode with breakdown of 6.5 ~ 7V can be selected. During normal operation, the transient diode does not work and is quite open circuit; When there is an instantaneous high voltage pulse in the working voltage, the transient diode is clamped at about 9V at the moment of high voltage pulse. This instantaneous 9V voltage is safe for the circuit working at 5V. When the high voltage pulse passes, the transient diode is quite open again.