Characteristics of Power Semiconductor Devices
- Diode – Current ratings from under 1 A to more than 5000 A. Voltage ratings from 10 V to 10 kV or more. The fastest power devices switch in less than 20 nanoseconds, while the slowest require 100 microseconds or more. The function applies in rectifiers and DC-DC circuits.
- BJT – (Bipolar Junction Transistor) Conducts collector current (in one direction) when sufficient base current is applies. Power device current ratings from 0.5 A to 500 A or more; voltages from 30 V to 1200 V. Switching times from 0.5 microseconds to 100 microseconds. The function applies to DC-DC circuits; combinations with diodes are used in inverters.
- FET – (Field Effect Transistor) Conducts drain current when sufficient gate voltage is applied. Power FETs have a parallel connected reverse diode by virtue of their construction. Ratings from about 1 A to about 100 A and 30 V up to 1000 V. Switching times are fast, from 50 nanoseconds or less up to 200 nanoseconds. The function applies to DC-DC conversion where the FET is in wide use, and to inverters.
- SCR – (Silicon Controlled Rectifier) Conducts like a diode after a gate pulse is applied. Turns off only when current becomes zero. Prevents current flow until a pulse appears. Ratings from 10 A up to more than 1000 A, and from 200 V up to 6 kV. Switching requires 1 microsecond to 100 microseconds. Widely used for controlled rectifiers.
- GTO – (Gate Turn-Off SCR) An SCR which can be turned off by sending a negative pulse to its gate terminal. Can substitute for BJTs in applications where power ratings must be very high. The ratings approach those of SCRs, and the speeds are similar as well. Used in inverters rated beyond about 100 kW.
- TRIAC – A semiconductor constructed to resemble two SCRs connected in reverse parallel. Ratings from 2 A to 10 A and 200 V to 800 V. Used in lamy dimmers, home appliances, and hand tools. Not as rugged as other device types.
- IGBT – (Insulated Gate Biploar Transistor) A special type of power FET that has the function of a BJT with its base driven by a FET. Faster than a BJT of similar ratings, and easy to use. Ratings form 10 A to more than 600 A, with voltages of 600 V up to 1200 V. The IGBT is popular in inverters from about 1 kW to 100 kW.
- MCT – (MOSFET-Controlled Thyristor) A special type of SCR that has the function of a GTO with its gate driven from an FET. Much faster than conventional GTOs, and easier to use. These devices are entering the market after several years of development.