Shindengen Electric MFG.CO.,LTD

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6.6.2 Oscillation stop circuit in case of low voltage input

This protection circuit prevents input from a 100 V group

power source to a 200 V group power supply. The circuit

monitors input voltages. On detecting an input of 100 V, the

circuit stops the oscillation of the MR4000 series. On

detecting an input of 200 V, the circuit allows regular

oscillation.

(1)

Circuit configuration

The circuit consists of a transistor Q1 that short-circuits

the input voltage detection resistor and the F/B pin (Pin 2),

a transistor Q2 that turns Q1 off, and a zener diode that

corrects for variations in VBE of Q2 and temperature

characteristics.

(2)

Circuit operation

The transistor Q1 short-circuits the F/B pin (Pin 2) of the

MR4000 Series until the input voltage Vin exceeds 138

V (a maximum voltage in the 100 V group), thereby

keeping the MR from oscillating. When Vin reaches 170

V (a minimum voltage in the 200 V group), Q2 is turned

on, turning Q1 off. The MR4000 Series begins

oscillating.

(3)

Problem

Efficiency is reduced during standby. Standby characteristics are decreased due to the current required for the

input voltage detection circuit and the current flowing to Q1 and Q2. If the resistor R1 is set to 56 kΩ or less, the

IC can not start up.

(4)

Precautions

If resistor R1 is set to 56 kΩ or less, the IC may not start up.

(Pin 4) of the MR4000 Series for other purposes.

6.6.3 Remote ON/OFF circuit for MR4000 Series

The oscillation of MR4000 Series devices can be turned on and off with

an external ON/OFF signal.

(1)

Circuit configuration

The circuit consists of a transistor that short-circuits the F/B pin (Pin 2)

and an external ON/OFF signal on the primary side. The external

signal can be input from the secondary side using a photocoupler

instead of the transistor.

(2)

Circuit operation

Upon receipt of the external signal, the transistor is turned on, short-

circuiting the F/B pin (Pin 2) and halting the power supply. When a

low external signal is input, the transistor is turned off, and

oscillation resumes.

(3)

Problem

If the power supply has been turned off by the external signal, the built-in startup circuit will continue charging

10kΩ

0.033μ F

C106

D112

IC111

2

4

3

9

C113

2SC945

R1

62kΩ

2SC945

8.2V

39kΩ

360kΩ

360kΩ

Q1

Q2

Fig. 6.20 Oscillation stop circuit in case of low

voltage input

Fig. 6.21 MR4000 Series ON/OFF

circuit

6. Supplementary design information