Sharp Z-810 Service Manual page 91

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When the output voltage falls below the specified level under
overload state, the voltage in the additional winding of the primary
side also falls accordingly to fall the VIN pin voltage below the
operation start voltage. Therefore, the VIN pin voltage rises again
and starts operation at the operation start voltage, performing
intermittent operations.
3) Overheat protection circuit
When the frame temperature of hybrid IC (IC802) exceeds 150°C
(TYP), this circuit actuates the latch circuit.
When the latch circuit is actuated, the oscillation output is kept
LOW to stop the power circuit. At that time, the VIN pin voltage
rises and falls between 10V (TYP) and 16V (TYP).
4) Overvoltage protection circuit
When the VIN pin voltage exceeds 22.0V (TYP), this circuit ac-
tuates the latch circuit.
It basically functions to protect against an overvoltage of the VIN
pin in the control circuit. Since, however, the VIN pin voltage is
supplied from the transformer additional winding and it is propor-
tional to the output voltage, it operates also against an overcurrent
in the primary side when the control circuit is opened.
(6) Secondary side rectifying/smoothing output circuit
The output from the transformer is passed through the rectifying
diode and the smoothing diode to be outputted. The component parts
numbers of the VB (+24V) are rectifying diode D802, and smoothing
capacitors C803 and C804. The component parts numbers of the
VBS (+14V) are diode D801 and smoothing capacitor C802.
As stated above, the VB (+24V) is used to stabilize the output as the
master circuit. The VBS uses the 3-terminal regulator of +8V in the
main PWB. Therefore, the instable voltage is in the range of 12.0V ∼
16.0V.
(7) Power ON/OFF circuit
This circuit turns OFF the switching power control IC (IC802) by the
signal from the main PWB. In the auto shut-down mode, oscillation of
the switching power is stopped to reduce power consumption.
When the /SWPEN signal is HIGH (+5V), the switching power is
turned on. When LOW, OFF (stopped.)
The VIN pin voltage of control IC (IC802) is decreased to the oscilla-
tion stop level by the /SWPEN signal through the photo coupler
(PC801), and the OCP/FB pin voltage is raised to the oscillation stop
voltage, stopping the control IC (IC802).
12 – 14
Published in Heiloo, Holland.
1/11/16