Zener/Transient Voltage Suppressor Diodes

Fly back diodes are helpful for high inductance devices, but they do not solve all problems. This is mostly because the power supply cables and traces have inductance as well, which makes the resulting EMF global to everything connected to Vin and GND. Zener and TVS diodes become shunts to ground when a voltage higher than the rated standoff voltage is presented. Zener diodes are often sufficient for ``clamping'' excess voltage (mostly due to inductor related EMF). If response time is critical, TVS diodes are specially designed to handle fast and big spikes.

The following diagram demonstrates how to set up a zener or TVS diode for shunting excess voltage. Note that you must match the zener or TVS diode according to your supply voltage.

Figure 8.2: Protection from Sudden Drain of Supply Voltage