Datasheet

UG-320 Evaluation Board User Guide
Rev. A | Page 6 of 48
QA1
QB1
QR1
QA2
QB2
QR2
SFW1
SFW2
I
QA1
I
QB1
I
LO1
I
LO1
+
I
LO2
I
QA2
I
QB2
I
LO2
V
Tp1
V
Tp2
D
D
D
D
t
t
t
t
t
t
t
10180-002
t
t
t
t
t
0
t
1
t
2
t
3
Figure 3. Summary of Key Waveforms for I2SF Topology
The key waveforms are illustrated in Figure 3. For the first
phase of the two-switch forward converter, the operation can
be simplified into three modes:
• Energy transfer stage (t
0
to t
1
): Both primary-side switches
(QA1, QB1) and the secondary-side rectifier switch (QR1)
are turned on and energy is transferred from input to
output
• Transformer reset stage (t
1
to t
2
): In this stage, two
primary-side diodes (or body diodes) conduct and apply
reversed input voltage to the transformer winding to reset
the transformer, while the secondary side is freewheeling
(SFW2 is on).
• Dead time stage (t
2
to t
3
): When the transformer is com-
pletely reset, the converter goes to the dead time stage with
no current in the primary side, while the secondary-side
current continues to freewheel.
The second phase operates in a similar pattern but with a 180°
phase shift in the PWMs.