Gc, And Gd Boards - Sony VPL-PX32 Service Manual

3-12-7. GB, GC, and GD Boards
1. Structure
The GB, GC, and GD boards are each composed of the DC-DC converter for step-down voltage as
shown below.
GB board : 5.9 ± 0. 3V→3.3 ± 0.3 V
GC board : 9.0 ± 2.0 V→5.0 ± 0.3 V
GD board : 17.5 ± 0.4 V→10.6 ± 0.3 V
2. Operations of the DC-DC Converter
As the structure of each DC-DC converter is more or less the same, the basic circuit operations are
described here.
BATTERY VOLTAGE
4.5V
SECF B
+2.505V
AT 100µA
REF
GND
ON/OFF
SHDN
SS
Fig. 6 shows the DC-DC converter control circuit structure. This converter adopts the step-down
chopper method in which the input voltage is directly switched by two MOS-FETs.
In moderate loads, the DC-DC converter sets into the idling mode and skips most of the internal
oscillator pulses to decrease the switching frequency and reduce MOS-FET switching losses.
In heavy loads, the converter controls the MOS-FET pulse width used for switching, and turns ON
the High side MOS-FET only for the time determined by the duty ratio.
When the MOS-FET at the High side goes OFF, the Low side MOS-FET turns ON after 60 ns. The
Low side MOS-FET maintains the ON state until the current flowing to the L inductor zero-crosses.
The aim of these operations is to attain high efficiency in both moderate and heavy loads.
3-22
TO
V+
CSL
+5V LIHEAR
REGULATOR
SHDH
PW
LOGIC
+2.505V
REF
PWN
CONPARATOR
LPF
3.3V FB
60kHz
5V FB
ADJ FB
4V
1V
SYNC
Fig. 6 DC-DC Converter Control Circuit
+5V AT 5mA
OUT
VL
BST
High side MOS-FET
DH
LX
DL
P GND
Low side MOS-FET
CSH
CSL
FB
MAIN
L OUTPUT
C
VPL-PX32