AN-9008 データシートの表示（PDF） - Fairchild Semiconductor

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AN-9008

The Use of QFETs in a Flyback Converter

Fairchild Semiconductor 

:

QFET

FQP7N60

Figure 1: Gate Charge Improvement

Balanced with gate charge improvement, the on-resistance [Rds(on)] goes down by about 20 per-

cent with respect to previous devices versus drain current. Figure 2 shows the improvement of on-

resistance in a QFET compared with a MOSFET.

1.10

Conventional MOSFET

QFET (FQP7N60)

1.05

1.00

0.95

0.90

0.85

0.80

0.75

0.70

1

2

3

4

5

6

7

Drain Current : Id [A]

Figure 2: On-resistance Improvement vs. Drain Current

The combined improvement of gate charge and on-resistance in this 60 watt flyback converter

leads to a more efficient system because of the reduced turn-off conduction loss. It is worth

emphasizing that QFETs offer designers significant improvements in terms of lower overall system

cost due to lower gate driver requirements, a smaller heat sink, and narrower PCB. Table 1 illus-

trates the features which are useful in flyback converters and other applications.

Table 1: Qg and Rds(on) Improvements

Voltage Rating

600V

600V

Device

Conventional Part

FQP7N60(QFET)

On-resistance

1.2 Ω

1.0 Ω

Gate Charge

65 nC

38 nC

Package

TO-220

TO-220

Rev D, July 2000

2

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