Transcript Power MOSFETs • Two Types – Depletion Type

Power MOSFETs
• Two Types
– Depletion Type
• Channel region is already diffused between the
Drain and Source
• Deplete, or “pinch-off” the Channel
– Enhancement Type
• No channel region exists between the Drain and
Source
• “Invert” the region between the Drain and Source
to induce a channel
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Depletion MOSFET
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N-Channel Depletion MOSFET
Normally Reverse-Bias the Gate-Source Junction
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Enhancement MOSFET
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N-Channel Enhancement MOSFET
The Gate-Source Junction will be Forward-Biased
The bias voltage must be greater than a “threshold” voltage
A Channel region is induced between the Drain and Source
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Drain Characteristics
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Steady-State Characteristics
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Switching Characteristics
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Equivalent Circuit
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Switching Model
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Switching Waveforms and Times
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Turn-on Delay, td(on) = time to charge the input
capacitance to VT
Rise time, tr = Charging time to charge the input
capacitance to the full gate voltage, VGSP in order to drive
the transistor into the linear region of operation
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Turn-off delay time, td(off) = time for the input capacitance to
discharge from “overdrive” voltage V1 to pinch-off.
VGS must decrease significantly for VDS to rise.
Fall time, tf = time for the input capacitance to discharge
from pinch-off to the threshold voltage.
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