what's the difference between 1N5402, HER502, and FR502 diodes?

[Sukhbinder]

what's the difference between 1N5402, HER502, and FR502 diodes?
The 1N5402 is a 3A 100V general purpose rectifier diode.
The HER502 is a 3A 100V high efficiency rectifier diode.
The FR502 is a 3A fast recovery diode.
The fast recovery diode is used for damping the reverse EMF in relays or other inductive devices like motors, chokes, etc.
The HER502 and 1N5402 are rectifier diodes but i can't seem to understand the difference between the a general purpose rectifier and a high efficiency rectifier. can one use the high efficiency rectifier as a fast recovery diode? what are schottky diodes used for? need some light on these features.
thanx  :D

[Herman the German]

Hi Sukhbinder,

I guess there is no difference in general purpose rectifier diodes and high efficiency ones.

The manufacturers might call a general purpose rectifier a "fast rectifier" diode or what so ever.

Fast recovery diodes can normally stand multiples of the rated current being pulsed. At high switching frequencies this might become important, e.g. driving a stepper motor to it's rpm limits.

I doubt you can use a high efficiency diode as a fast recovery diode.

Schottky diodes generally have a lower voltage drop than silicium type rectifier diodes. Used as an "idiot's diode" to prevent false polarity in a circuit they drop the supply voltage by 0.4V. Rectifier diodes do 0.7V.

HtG

[Sukhbinder]

Thanks HtG for the reply. I knew about the fast recovery diodes and their use but was a bit confused about the general purpose rectifier and high efficiency rectifier. May be the high efficiency rectifiers are more preferred in high frequency rectifiers (may be in a switched supply or so). Schottky diodes surely have a lower drop out voltage than silicon diodes. (germanium diodes had lower drops of 0.3V but could not handle high currents like silicon diodes and had a larger reverse leakage current than Si diodes. Also the Germanium devices could not be used at high temperatures or high powers, Si devices work easily at 80C with breakdown till 150C)