1-3. CA3 CIRCUIT DESCRIPTION

1. OutlineThis is the main CA3 power block, and is comprised of the following blocks.Switching controller (IC521)Analog system 5.0 V power output (L5201, Q5203, D5201, C5206)Backlight power output (L5101, Q5102, D5101, C5106)2. Switching Controller (IC521)

This is the basic circuit which is necessary for controlling the power supply for a PWM-type switching regulator, and is provided with one built-in channel. Feedback from 5 V (A) power supply output is received, and the PWM duty is varied so that each one is maintained at the correct voltage setting level.

2-1. Short-circuit protection circuit

If output is short-circuited for the length of time determined by the condenser which is connected to Pin (2) of IC521, all output is turned off. The control signal (P ON, P(A) ON and LCD ON) are recontrolled to restore output.

3. Switching Controller (IC511)

This is the basic circuit which is necessary for controlling the power supply for a PWM-type switching regulator, and is provided with one built-in channel. Feedback from 10 mA (L) power supply output is received, and the PWM duty is varied so that each one is maintained at the correct current setting level.

3-1. Protection circuit

If output is short-circuited for the length of time determined by the condenser which is connected to Pin (2) of IC511 the output is shorted out or the backlighting is open (there is no connection between CN512 and the backlight unit), output will turn off. all output is turned off. The control signal (P ON, P(A) ON and LCD ON) are recontrolled to restore output.

4. Analog system 5.0 V Power Output

5 V (A) is output. Feedback is provided to the swiching controller (Pin (1) of IC521) so that PWM control can be carried out.

5. Backlight Power Output

10 mA (L) is output. The backlighting turns on when current flows in the direction from pin (1) to pin (2) of CN512. At this time, a feedback signal is sent from pin (2) of CN512 to pin

(1)of IC511 so that PWM control is carried out to keep the current at a constant level (10 mA).

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