7004 Datasheet, PDF (3/12 Pages) Bourns Electronic Solutions – Network Interface Device

V_GS
V_DS
I_D(Q1)
I_D1
PWM'ED EDGE
-V_SPIKE
-V_IN + V_FB
-V_IN
V_FLBK
VSAT
SW
ON
V_{SW 0 VIN}
TIME
I_{PRI 0}
I_PK
TIME
I_{SEC 0}
TIME
Figure 2. Typical waveforms for the flyback regulator.
Single Transistor Forward Converters
The forward converter achieves much better transformer utilization than the flyback design
since in theory, the transformer stores no energy. There is an extra inductor in the output
power path and an additional diode as well. Single transistor forward converters are useful in
48V system designs, up to 150 watts or so. A similar problem exists in the forward converter as
in the flyback design because the drain voltage is inherently unconstrained. Leakage
nductance in the power transformer will produce large voltage spikes that must be snubbed or
clamped.
©2001 Fairchild Semiconductor Corporation
3
Rev. A, June 2001