Philips DVD-712, Service Manual, Page: 39 / 61

Alignments
GB 55 DVD712-722 8.
8. Alignments
No electrical alignments available
9. Circuit Descriptions And List Of Abbreviations
9.1 Current Mode Power Supply
9.1.1 Introduction
The switch mode power supply ( SMPS ) is mains isolated.
The control IC 7145 ( UC 3842A ) produces pulses to drive
the power switch, Mosfet 7125.
Power supply regulation is achieved by using duty cycle
control at fix frequency ,of approximately 58KHz ,determined
by the RC timing components.
9.1.2 General Description Of UC 3842A
The UC 3842 is a high performance fixed frequency current
mode controller that is specifically designed for off-line and
DC-to-DC converter application. This integrated circuit
feature a trimmed oscillator for precise duty cycle control, a
temperature compensated reference, high gain error
amplifier, current sensing comparator and a high current
totem pole output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and
reference undervoltage lockouts each with hysteresis, cycle
by cycle current limiting, programmable output deadtime and
a latch for single pulse metering.
A representative Block diagram and Pin function description
is shown in Fig 9-1 and Fig 9-2 respectively.
9.1.3 Block Diagram
Figure 9-1
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