The conventional forward converter. Max v ds = 2 V g + ringing Limited to D < 0.5 On-state transistor current is P / DV g Magnetizing current must operate in DCM Peak transistor voltage occurs during transformer reset
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Transistors are driven in usual half-bridge manner:
Vb can be viewed as a flyback converter output. By use of a current-bidirectional switch, there is no DCM, and LM operates in CCM.
Max vds = Vg + Vb = Vg /D’
which is less than the conventional value of 2 Vg when D > 0.5
This can be used to considerable advantage in practical applications where there is a specified range of Vg
Peak vds = 2Vg + ringing = 700 V + ringing
Let’s let max D = 0.5 (at Vg = 270 V), which is optimistic
Then min D (at Vg = 350 V) is(0.5)(270)/(350) = 0.3857
The on-state transistor current, neglecting ripple, is given by ig = DnI = Did-on
with P = 200 W = Vg ig = DVg id-on
So id-on = P/DVg = (200W) / (0.5)(270 V) = 1.5 A
Basic switch network reduces to:
(if the blocking capacitor is an ac short circuit, then we obtain alternately switching transistors—original MOSFET plus the auxiliary transistor, in parallel. The tank L and C ring only during the resonant transitions)
The upper transistor, capacitor Cb, and tank inductor are added to the hard-switched PWM boost converter. Semiconductor output capacitances Cds are explicitly included in the basic operation.