A protection diode is a type of Zener diode. Zener diodes can be used not only as protection diodes but also as constant-voltage regulators. Protection diodes are specifically designed to protect electronic circuits from ESD and other transient pulses. In contrast, Zener diodes for constant-voltage regulation remain conducting in breakdown mode.
Protection diodes are used as voltage clampers for surge protection. These diodes are designed to conduct in the event of excessive voltage being applied to a circuit.
Diodes for constant-voltage regulation
The voltage that appears across a diode when a small current (IZ) is passed from cathode (K) to anode (A) is used as a constant-voltage source (VZ). The amount of power that can be applied is constrained by the permissible power dissipation of the diode and the board on which it is mounted.