
AN372
AN372REV1 9
The buck stage is supplied by the boost output voltage. The boost output voltage is regulated within 10% by
the boost stage. The buck control loop regulates the output current as long as the peak current has sufficient
margin to rise 10% at the lowest boost output voltage. Figure 4a and Figure 4b show idealized waveforms of
the FET Q4 drain voltage and drain current and the diode D3 current.
Area = N ު V
OUT
ު T2
Area = V
OUT
ު T2
Area = (V
BST
- V
OUT
)
ު T1
V
BST
V
ZERO
N ު V
OUT
V
OUT
t
V
Reflected
Figure 4a. FET Drain Voltage
Figure 4b. Current Through FET Q4 and Diode D3
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