MS1003SH datasheet(29/41 Pages) SHINDENGEN

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MS1003SH･MS1004SH

Application Note Ver.2.2

SHINDENGEN ELECTRIC MFG. CO. , LTD

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3) D102

This diode sets the Z/C pin to low to activate normal mode.

As described in Section 3.2.1, the on-trigger circuit detects the Z/C pin voltage when it reaches VZ/C

(0.25 V). Thus, the diode should not reduce the voltage below VZ/C. Make sure the diode has

adequate VF to secure VZ/C.

5.5.2 Design procedure for F/B pin

(1) Basic circuit

The diagram to the right shows the basic circuit. PH101 is

a photocoupler for constant voltage control. R107 and

C107 are noise reduction components.

C107 has a capacitance between 470 pF and 2,200 pF. Set

the initial design value to 1,000 pF. R107 is set between 39

kΩ and 47 kΩ. Normally, it should be set to 47 kΩ. If the

resistance falls below 39 kΩ, the timer latch function may

be disabled.

(2) Protection

PH101 may exhibit insulation breakdown during a short

circuit test. If so, protect the circuit using a zener diode, as

shown to the right. A zener diode for 10 V or greater

should have negligible effect on IC functions for normal

use.

(3) Phase compensation of F/B pin

C107 is used not just to reduce noise, but to adjust

feedback response. However, in a large-capacity or

multi-output power supply, phase compensation by the

secondary control circuit may be inadequate.

If so, add a circuit between the F/B pin and the GND pin,

as shown to the right. Doing so can resolve various issues,

including hunting.

Refer to the following table to determine constants.

Initial design value

R303

4.7 kΩ

C301

0.1

F

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