5

Rev D, July 2000

Figure 5 compares the waveforms of a conventional MOSFET with the new QFET(FQP7N60) at

turn-off without the additional clamped circuit (R5, C6, and D2), and the high conduction diode (D4)

for gate discharging (refer to Figure 3).

Note that the switching time of the QFET is faster than that of the conventional MOSFET because

of the reduction of gate charge by at least 45 percent. Figure 6 shows the difference in turn-off loss

between both MOSFETs without clamped circuits and the conduction diode, D4. The turn-on loss

in the crossover losses is very small and can be negligible. The turn-off loss period is due to the

finite switching time of the MOSFET which is directly related to the gate charge.

Figure 6: Turn-off Loss Improvement

Conventional

MOSFET

QFET

Id(0.5A/div)

Vds(100V/div)

/div

Conventional

MOSFET

QFET

/div