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For power semiconductor device
Semiconductor device

Semiconductor devices are electronic components that exploit the electronics properties of semiconductor materials, principally silicon, germanium, and gallium arsenide....
 (such as BJT, MOSFET
MOSFET

The metal?oxide?semiconductor field-effect transistor is a device used to amplify or switch electronic signals. The basic principle of the device was first proposed by Julius Edgar Lilienfeld in 1925....
, thyristor
Thyristor

The thyristor is a Solid state semiconductor device with four layers of alternating N-type semiconductor and P-type semiconductor material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward biased ....
 or IGBT) a safe operating area (SOA) is defined as the voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 and current conditions over which the device can be expected to operate without self-damage.

SOA is usually presented in transistor datasheet
Datasheet

A datasheet is a document summarizing the performance and other characteristics of a component , a sub-system or software in sufficient detail to be used by a design engineer to design the component into a system....
s as a graph with VCE (collector-emitter voltage) on the abscissa and ICE (collector-emitter current) on the ordinate; the safe 'area' referring to the area under the curve.






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For power semiconductor device
Semiconductor device

Semiconductor devices are electronic components that exploit the electronics properties of semiconductor materials, principally silicon, germanium, and gallium arsenide....
 (such as BJT, MOSFET
MOSFET

The metal?oxide?semiconductor field-effect transistor is a device used to amplify or switch electronic signals. The basic principle of the device was first proposed by Julius Edgar Lilienfeld in 1925....
, thyristor
Thyristor

The thyristor is a Solid state semiconductor device with four layers of alternating N-type semiconductor and P-type semiconductor material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward biased ....
 or IGBT) a safe operating area (SOA) is defined as the voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 and current conditions over which the device can be expected to operate without self-damage.

SOA is usually presented in transistor datasheet
Datasheet

A datasheet is a document summarizing the performance and other characteristics of a component , a sub-system or software in sufficient detail to be used by a design engineer to design the component into a system....
s as a graph with VCE (collector-emitter voltage) on the abscissa and ICE (collector-emitter current) on the ordinate; the safe 'area' referring to the area under the curve. The SOA specification combines the various limitations of the device — maximum voltage, current, power, junction temperature, secondary breakdown — into one curve, allowing simplified design of protection circuitry.

Often, in addition to the continuous rating, separate SOA curves are provided for short duration conditions (1 ms pulse, 10 ms pulse etc.).

SOA specifications are incredibly useful to the design engineer working on power circuits such as amplifier
Amplifier

Generally, an amplifier or simply amp, is any machine that changes, usually increases, the amplitude of a Signal . The "signal" is usually voltage or current....
s and power supplies
Power supply

Power supply is a reference to a source of electrical power. A device or system that supplies electrical or other types of energy to an output External electric load or group of loads is called a power supply unit or PSU....
 as they allow him/her to quickly determine the conditions under which a design will catch fire, allowing the design of appropriate protection circuitry and/or selection of a more capable device. SOA curves are also important in the design of foldback
Foldback

Foldback may refer to:In technology:...
 circuits.

The most common form of SOA protection used with BJTs senses the collector-emitter current with a low-value series resistor; the voltage across this resistor is applied to a small auxiliary transistor that progressively 'steals' base current from the power device as it passes excess collector current.

This approach is effective but not bullet-proof. In practice it is very difficult to design a protection circuit that will work under all conditions, and it is left up to the design engineer to weigh the likely fault conditions against the complexity and cost of the protection.

Types of safe operating area

  • Reverse bias safe operating area (or RBSOA) is SOA when turning the device into the off-state. The RBSOA may be different from generic SOA, for example for IGBTs, upper half corner of the RBSOA is progressively cut out which reduces the RBSOA as the rate of change of the collector to emitter voltage across the device, dVce/dt, is increased.


  • Forward bias safe operating area (or FBSOA) is SOA when turning the device into the on-state.


See also

  • Derating
    Derating

    Derating is the technique employed in power electrical and electronic devices wherein the devices are operated at less than their rated maximum power dissipation taking into consideration the case/body temperature, ambient temperature and the type of cooling mechanism used....