MS1003SH datasheet(30/41 Pages) SHINDENGEN

30 / 41 page

MS1003SH･MS1004SH

Application Note Ver.2.2

SHINDENGEN ELECTRIC MFG. CO. , LTD

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(4) Additional circuit to F/B pin

When adding a circuit to the power supply circuit due to load setting conditions or for other reasons, be

careful to avoid disabling the timer latch function. Disabling the timer latch will affect power supply

performance.

5.5.3 Design of OCL pin

(1) Basic circuit

The diagram to the right shows the basic circuit.

The circuit consists of R104 for primary current

detection and a filter circuit comprising R103 and C106.

R104: Resistance required in Section 5.4

C106: Initial design value of 220 pF

Design values from 220 pF to 3,300 pF

R103: Initial design value of 100 Ω

Design values from 100 to 470 Ω

Increase the constants if switching noise is significant

and may lead to malfunctions.

(2) Protection for large output power

If switching noise is significant—for instance, because output power is large—a high negative voltage

may be applied to the OCL pin. Since the MS100xSH series are single power supply ICs, a negative

voltage may damage the IC or cause malfunctions.

The following diagram shows a circuit that incorporates a feature to protect the OCL pin against

negative voltages. The added diode D301 should have small VF (a Schottky barrier diode is

recommended) and should be connected as close as possible to the pin.

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