AN9008 Datasheet, PDF (4/9 Pages) Fairchild Semiconductor – The Use of QFETs in a Flyback Converter

Table 2: Power Supply Specifications
1. Operating mode
2. Input voltage (V_in)
3. Switching frequency (f_sw)
4. Output voltage (V_out)
5. Efficiency (η)
:
Flyback Discontinuous Mode
:
180 VAC to 265 VAC (50Hz/60Hz)
:
80 kHz
:
A. 160V ± 5% 0.3A
B. 15V ± 5% 0.8A
:
75%
This flyback converter was tested in rated conditions of 220VAC input voltage, 80kHz switching
frequency, and 60W output power.
Figure 4 shows the waveforms for rated operating conditions using the QFET(FQP7N60) as the
switching device. The QFET is driven by a gate-source voltage of 15V and the voltage spike
across the drain-source terminal is adequately clamped to about 500V by an additional clamp cir-
cuit during off-time.
Vgs(5V.div)
Id(1A/div)
Vds(250V/div)
Figure 4: Operating Waveforms at Rated Conditions (V_in=220VAC, P_out=60W)
Rev D, July 2000
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