Switching Controller (Ic501); Shot-Circuit Protection Circuit; Digital 5V And Analog System Power Output; Digital 3.25V System Power Output - Epson PhotoPC 850Z Service Manual

EPSON PhotoPC 850Z

2.2.3.2 Switching Controller (IC501)

This is the basic circuit which is necessary for controlling the power supply for a
PWM-type switching regulator, and it is provided with four built-in channels.
Only CH1 (digital 5V, analog system), CH3 (LCD system), CH2 (digital 3.25V),
and CH4 (backlight) are used. Feedback from 5.1V (D) (CH1), 3.0V (D) (CH2),
5.3V (L) (CH3), and 6.3-8.9V (L) (CH4) power supply outputs is received, and
the PWM duty is varied so that each one is maintained at the correct voltage
setting level.

2.2.3.3 Shot-Circuit Protection Circuit

If output is short-circulated for the length of time determined by the condenser
which is connected to Pin (17) of IC501, all output is turned off. The control
signal (P ON, P(A) ON, and LCD ON) are re-controlled to restore output.

2.2.3.4 Digital 5V and Analog System Power Output

5.1V (D), 15.2V (A), -7.7V (A), and 5.1V (A) are output. Feedback for the 5.1V
(D) is provided to the switching controller (Pins (29) of IC501) so that PWM
control can be carried out.

2.2.3.5 Digital 3.25V System Power Output

3.25V (D) is output. Feedback is provided to the switching controller (Pin (26)
of IC501) so that PWM control can be carried out.

2.2.3.6 LCD System Power Output

5.3V (L), 12.4V (L), and 15V (L) are output. Feedback for the 5.3V (L) is
provided to the switching controller (Pin (11) of IC501) so that PWM control can
be carried out.

2.2.3.7 Backlight Power Supply Output

The power which is input to the inverter transformer (T5003) is controlled by
means of Q5011, and 7.7V or 8.9V is output depending on the luminance
mode of the LCD panel.
Operating Principles Operating Principles of Circuit Boards
Revision A
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