Comparison of Power MOS and Bipolar Power Transistors

MOS BIPOLAR
Majority-carrier device Minority-carrier device
No charge-storage effects Charge stored in the base and collector
High switching speeds, less temperature sensitive than bipolar devices Low switching speed, temperature sensitive
Drift current (fast process) Diffusion current (slow process)
Voltage Driven Current Driven
Purely capacitive input impedance; no DC current required Low input impedance; DC current required
Simple drive circuitry Complex drive circuitry (resulting from high base current requirements)
Predominently negative temperature coefficient on resistance Positive temperature coefficient of collector current
No thermal runaway Thermal runaway
Devices can be paralleled with some precautions Devices cannot be simply paralleled because of VBE matching problems and local current concentration
Less susceptible to second breakdown Susceptible to second breakdown
Square-law I-V characteristics at low current; linear I-V features at high current Exponential I-V characteristics
Greater linear operating and fewer harmonics More intermodulation and cross-modulation products
Low on-resistance (low saturation voltage) because of conductivity modulation of high resistivity drift region High on-resistance and therefore larger conduction loss
Drain current proportional to channel width Collector current approximately proportional to emitter stripe length and area
Low transconductance High transconductance
High breakdown voltage as the result of a lightly doped region of a channel-drain blocking junction High breakdown voltage as the result of a lightly doped region of a base collector blocking junction
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