4 TVS Diodes and Zener Diodes

RC snubbers are great for filtering transients caused by hot-plugging adapters which maintain a steady dc voltage level to power an IC. However, if the power source has large voltage swings, for instance like a battery at the output of a battery charger that frequently supplements a system transient load, the RC snubber is not the best choice. Even though more costly than an RC snubber, a TVS or zener diode can be used to suppress voltage spikes from adapter hot plug.

A transient-voltage-suppression diode, or TVS diode, is designed to protect electronic components from voltage spikes. The TVS diode begins to operate once the voltage on the diode exceeds the avalanche breakdown potential. A TVS diode resets once this voltage goes away. A TVS diode can be both unidirectional or biderectional. A graph of a TVS diode's I-V curve is shown in Figure 4-1

Zener diodes work the exact same way as TVS diodes do and zener diodes follow a similar curve. The only difference is that TVS diodes are designed to have a faster response time and a higher surge current conduction capability.

To select a TVS diode, first know the maximum safe working voltage of the IC pin needing protection and the minimum harmful voltage. Chose the reverse working voltage to be above the maximum safe working voltage of the circuit and the clamping voltage to be below the minimum harmful voltage.

To select a zener diode, know the maximum working voltage and minimum harmful voltage. Chose the zener voltage to be between the max working voltage and the min harmful voltage.