MM1548 データシートの表示（PDF） - Mitsumi

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MM1548

Secondary Control for Energy-Saving AC Adaptor

Mitsumi 

MITSUMI

Secondary Control for Energy-Saving AC Adaptor MM1548

Operation

Voltage between VCC and OUT(200mV)

RLS

470Ω

Supply transistor

RLB

100Ω

VCC

CNT

OUT

Load current

200mV

Input/output difference control

Voltage drop detection

(V=4.6V)

ROS1

PC1

200mV Load current detection

Voltage drop detection

(VCC=3.5V)

REF

Overvoltage

detection

115mV Energy saving current detection

Constant voltage control

ROS2

(VCC, OUT=7V)

Energy saving mode

Normal mode

(VCC=5.1V)

Energy saving mode control

(3.5V :ON, 5.1V :OFF)

Photocoupler-turn-off(4.6V )

Constant current control

(CS=114.4mV)

(Io=520mA)

PO1 drive(Load 5kΩ)

PO1 drive

Photocoupler PC1 control

PO1

GND

CS

RCS

0.22Ω

Output

(+)

(–)

1. Operation of Blocks

1.1 Input/output difference control

In the normal mode that a load current is detected and the system supplies the load current through the

Supply Transistor (PNP type), MM1548 controls CNT current flowing into the base of Supply Transistor to

keep the differential voltage between VCC and OUT (Vce of Supply Transistor) at 200mV.

1.2 Load current detection and Energy saving current detection

When load current increases in energy saving mode and the differential voltage between VCC and OUT

exceeds VLSP1 (200mV), MM1548 changes to the normal mode, PO1 switches from open to low mode,

and the photocoupler PC1turns on. As a result, the system switches primary-side switching operation to

normal mode from disabled.

The switching voltage has following hysteresis if load current is increasing ( VLSP1) or decreasing

( VLSP2).

( hysteresis: VLSP1 = 200mV < > VLSP2 = 115mV)

When the differential voltage between VCC and OUT falls to VLSP2 (115mV), MM1548 changes to the

energy saving mode, and the photocoupler-turn-off circuit switches compulsory photocoupler current to

zero under the condition that load current is decreasing in normal mode and Vcc = 4.6V or more.

1.3 Voltage drop detection

When VCC voltage falls to 4.6V in the energy saving mode, MM1548 stops the photocoupler-turn-off circuit

operation to save consumption current of MM1548.

When VCC voltage falls to 3.5V in the energy saving mode, MM1548 changes to the normal mode.

As a result, Out voltage (output of secondary side) swings intermittent between 4.9V and 3.5V.

1.4 Constant current control

When load current is increasing in the normal mode, and the differential voltage between CS and GND

exceeds VCS1(114.4mV typ.), PO1 switches from open to low mode, and the photocoupler PC1 turns on. As

a result, MM1548 changes to the CC(constant current) mode, and the load current is controlled that CS

voltage keeps VCS1.

1.5 Constant voltage control

When MM1548 is in normal mode and isn't in constant current mode, it is in CV(constant voltage) mode,

and PO1 current is controlled that VCC voltage keeps 5.1V (equal to internal 1.25V: REF voltage).

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