The output or drain characteristic of N - Channel power MOSFET. When gate is made positive with respect to the source an N type channel is formed close to the gate. In this case N +type substrate and the N source terminal. When Vgs is zero or negative no channel exists and the drain current is zero with the increase in gate voltage the channel resistance is reduced and therefore the drain current ID increases thus the drain current ID remains fairly constant over a wide range of Vps levels. Drain terminal beings at the bottom of the power MOSFET. It can have a considerable large area for any given of the device which allows more power dissipation.
Figure output characteristics of N channel power MOSFET
When Vas is zero or negative and the drain is positive with respect to source the junctions between the P layer and the N layer is reverse biased. The depletion region at eh junction penetrates deep into the N layer and thus punch through from drain to source is avoided.
The lower most curve is for VGS ( Th.) when VGS< VGS(Th.) drain current is almost zero when VGS> VGS(Th.) the device is ON. This device has three regions ohmic region active region and breakdown region. The rising part of curve (from BDS= 0 to VDS= few volts) is the ohmic region. The device behaves as a resistor when operated in this region. The drain current is almost constant when the device operates in the active region.ehn BDS excess the rated value avalanche breakdown occur and the device is in the breakdown region. Vgs can be positive and negative. The characteristics of P channel power MOSFET are similar to those of N channel MOSFET except that the current directions and voltage polarities are reversed.