Different types of diodes and their applications.
Types of Power Diodes
- Standard diode (or) General purpose diode
- Fast recovery diode
- Schottky diode
1. General Purpose Diodes
These diodes have high reverse recovery time ( 25 micro seconds). Ratings from 1A/50V to 1000A/5000V. Switching speed : Upto 1 kHz. These diode consist of additional lightly doped n- epitaxial layer(drift region) that absorbs depletion layer formed due to reverse voltage. Applications: Low speed applications, battery charging, electric traction, electroplating, welding and uninterruptible power supplies(UPS)
2. Fast recovery diodes(switching diodes)
Reverse recovery time is less than 5 micro seconds. Ratings: 1A/50V to 100A/3000V. For voltage rating below 400V the epitaxial process used for diode fabrication. These diodes have fast recovery time, as low as 50 μsec. For voltage rating above 400V, diffusion process used for diode fabrication. Very high frequency applications. Applications: Choppers, inverters, commutation circuits, UPS, switched mode power supplies(SMPS), induction heating etc.,
3. Schottky diodes
A Schottky diode is a metal-semiconductor diode with an extremely fast switching speed and a low forward voltage drop. The anode is metal, and the cathode is semiconductor. A thin film of metal is placed directly on the semiconductor. In schottky diodes, the PN junction is eliminated. When schottky diode is forward biased, free electrons in n-material move towards the al-n junction and then travel through the metal(aluminium) to constitute the flow of forward current.
Since metal does not have any holes, this forward current is due to movement of electrons only. As the metal has no holes, there is no storage charge and no-reverse recovery time.(storage time is absent, turn off time is very small). Compared to a p-n junction diode, a Schottky diode can turn off significantly faster. Hence schottky diodes have high switching frequencies
Compared to p-n junction diode, a schottky diode has (i) Lower cut in voltage(0.2V) (ii) Higher reverse leakage current and (iii) Higher operating frequency. Reverse breakdown voltage of the schottky diode is 50V. (PN junction diode is 150V) . Forward current rating from 1A to 300A. Applications: High frequency instrumentation, low voltage converters, feedback, freewheeling diodes and switching power supplies, Radar systems, mixer and detectors in communication circuits.