Sony VPL-PX32 Service Manual page 46

Zero Current
Detector
Delay
RS Latch
Multiplier Input
Fig. 4 show a simple block diagram of the active filter control (IC2100). The current flowing to
MOS-FET (Q2100) is detected by the sense resistor (R2106). When this current reaches the threshold
value corresponding to the peak current flowing to the choke coil (L2100), the comparator turns OFF
the MOS-FET (Q2100). The threshold value is sent to the comparator as the product of the AC
voltage waveform and control amplifier output voltage V0. The MOS-FET (Q2100) maintains the
OFF state until the choke coil (L2100) and diode (D2108) current becomes zero. The output is
maintained at 358 ± 10 V by the PWM control of the switching. This output setting is performed by
the R2127 to R2133 voltage-dividing resistor.
4. Timer function
As a watchdog timer function is equipped inside the IC2100, no external oscillator is required. When
the current flowing to the choke coil (L2100) reaches zero and the drive output becomes OFF for
more than 620 µs, the timer automatically starts or restarts the pre-converter.
5. Internal over-voltage comparator
To prevent abnormal output voltages, the control IC (IC2100) is equipped with an over-voltage
comparator. This comparator turns ON at initial startup, when the load changes suddenly, and when
the output ripple increases. The over-voltage comparator monitors the peak output voltage of the
converter, and turns OFF the MOS-FET (Q2100) immediately when the reference value is exceeded.
The threshold value of the comparator is set to 1.08 V in the control IC (IC2100).
3-18
1.2V
1.6V
2.5V
UVLO
Reference Voltage
Source
Timer R
Current Sence Comparator
1.5V
Over Voltage Comparator
1.8V
Multiplier
GND Compensation
Fig. 4 Simple Block Diagram of IC2100
V
CC
Zero Current
6.7V
Detector IN/OUT
13V
16V
Drive Output
Current Sence
Input
Differential
Amplifier
Vref
Voltage Feedback
Input
Quick Stert
VPL-PX32