Types of Power Diodes

3 types of diodes:

standard or general-purpose diodes
fast-recovery diodes
Schottky diodes

General-purpose diodes: typically t_rr ~ 25μs, used for low-speed applications where recovery time is not critical (f < 1kHz), IF = less than 1A to several thousands of amperes, V_RB = 50V to ~5kV. Types: diffusion and alloyed. Alloyed rectifiers are cost-effective and rugged (for welding machines) with up to 300A and 1000V.

Fast-recovery diodes: normally t_rr < 5μs, used for applications where the speed of recovery is often critical importance, I_F = less than 1A to several hundreds of amperes, V_RB = 50V to ~3kV. Types: diffusion and epitaxial. Epitaxial diodes: <400V and as low as 50ns.

Schottky diodes: Advantages: low forward voltage drop, 0.3 to 0.4 V typically. Disadvantages: reverse leakage current > that of a pn junction diode and reverse biased breakdown voltage < 100V. In fact, a Schottky diode with relatively low forward voltage has relatively high leakage current, and vice versa. I_F = 1 - 100A. Suitable for low voltage applications.

Freewheeling Diodes
If an attempt is made to open the switch shown in the Figure below, the energy stored in the inductor will arc across the contacts of the switch, and could cause damage to the circuit components. Freewheeling diodes are placed across inductive loads to provide a path for the release of energy stored in the load when the load voltage drops to zero. Diode Dm is the freewheeling diode.