Familiar with the electronic element- MOSFET

A MOSFET is looked similar, although they have different packages, so we can’t tell the MOSFET model from its appearance. The common use package is: T0-252, T0-251, T0-220, T0-247, etc. according to different conducting ways, it can be divided into Channel enhancement and depletion, each of them can be divided into N-channel and P-channel.

In a power supply circuit, we usually use N-channel enhancement MOSFET.

A MOSFET has three pins, face the side of the screen print to yourself, grid electrodes, drain electrodes and source electrodes from left to right.

Working principle

  • N-channel enhancement MOSFET. At first, add a voltage between grid electrode and source electrode, the current pass from grid electrode to source electrode, after that drain electrode and source electrode turn on, at this time, plus an HD voltage between drain electrode and source electrode, high current can pass through the drain electrode and source electrode, end to GND.
  • P-channel enhancement MOSFET. It works just the opposite of N-channel enhancement MOSFET, it should add a voltage between the source electrode and grid electrode, after that plus an HD voltage between source and drain, the high current can pass through the source and drain, end to GND.

A MOSFET has three states, cutoff area, variable resistance area, constant current area.

Main parameter

  • Rated voltage(VDSS). When the voltage is zero between drain and source, the maximum voltage that MOSFET can sustain at room temperature. Generally, the rated voltage of MOSFET is 600V or 650V.
  • Rated current(ID). When the temperature of shell is 25℃, drain and source turn on( the voltage is 10V), between drain and source can withstand continuous current, but as the temperature of the shell rises, rated current drop down to 60% when the temperature of shell is 100℃, and the rated current drop down to 0 when the temperature of shell is 150℃.
  •  Resistance Rds(on). A room temperature, drain and source turn on(voltage is 10V), the resistance value between grid and source. The resistance Rds will be rise as the temperature rise, the high the temperature, the greater the resistance.
  • Drain and source turn-on threshold voltage(Vth). A critical voltage when drain and source turn on.
  • Interelectrode capacitance. Gate-source capacitance, gate-drain capacitance, and drain capacitance.

For example, a MOSFET: SVF10N60

  • Rated voltage(VDSS): 600V
  • Rated current(ID): 10A
  • Resistance Rds(on): 0.75R-1R (VGS = 10V ID = 10A)

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