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MM1548

Secondary Control for Energy-Saving AC Adaptor

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MITSUMI

Secondary Control for Energy-Saving AC Adaptor MM1548

1.6 Overvoltage detection

When VCC voltage or OUT voltage exceeds 7V (overvoltage), overvoltage detection circuit turn on.

As a result, PO1 sink current is controlled to turn on the photocoupler PC1, and system is protected from

overvoltage.

This circuit also detects negative voltage applied CS pin, and when it is detected, PO1 current is turned off

for overvoltage protection.

2. Design principles for each mode

AC adaptor output is controlled by following 4 mode under usage with MM1548.

Switching of each control mode is explained as follow.

Energy saving mode

(PO1:Open)

CV MODE

(PO1:Control)

Energy saving current detection (load detection release )

Load current detection

VCS(115mV typ.)

CC MODE

(PO1:Control)

CC MODE

Drop curve

(PO1:Control)

(115mV/RLS)

(200mV/RLS)

34mV/RCS

114.4mV/RCS

Load current [A]

2.1 for Output voltage

In MM1548 series, the output voltage can't be adjusted by external resistor, because referential voltage

terminal (REF pin) for adjustment is build in the chip.

Instead of voltage adjustment, you can chose output voltage by select the rank of MM1548 series.

Output voltage is lower 0.2V (equal to in-out differential control voltage) than 5.1V(equal to the value set by

ROS1 and ROS2).

[Formula]

Output voltage

= Vo – VLS

= {1+(ROS1/ ROS2)} 1.25 – VLS

= {1+(2460k/800k)} 1.25 – 0.2

= 4.9V

(Vo = 5.1V)

( VLS = 0.2V)

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