Service manual

CP-850FX Service Manual

Europe R&D

5.10.4 OCP/BD Terminal (Pin 7)

The functions of OCP/BD terminal are categorized as Overcurrent Protection (OCP), Bottom-

Skip, and Quasi-Resonant Operation control. Refer to item No. 8.5 for Bottom-Skip and Quasi-

Resonant operation.

8.4.1. Minus-Detection Type OCP Circuit

The OCP of the STR-W6700 series is pulse-by-pulse

type Overcurrent protection circuit, which detects the

peak value of the MOSFET drain current per pulse and

reverses oscillator output. As shown in Fig.14,

overcurrent detecting resistors, R5, R4, and C5 are

mounted externally. R4 and C5 construct the filter

circuit that prevents malfunctions caused by the surge

current generating at the MOSFET Turn-ON. As the

Overcurrent Protection Circuit operation (OCP), it turns

OFF the MOSFET at that time when OCP/BD terminal

threshold voltage reaches VOCPBD(LIM) by the

voltage generated at the overcurrent detecting resistor

R5 after the switching current flows at the MOSFET ON.

The threshold voltage VOCPBD(LIM) of the OCP/BD terminal is set at –0.95V (Typ). The OCP

circuit adopts the minus-detection circuit, which provides the detecting voltage VOCPM in the

MIC by dividing the voltage (between V1 and R5) with RB1, RB2, and R4. Since the RB1 and

RB2 are resistors incorporated in the HIC, taking the distributions of RB1 and RB2 (regulated as

IOCPBD in the specs) into consideration, the value of R4 is to be between 100 to 330 Ohms in

order to lower the influence from the distributions between RB1 and RB2.

Fig.14. Minus-Detection OCP

Circuit

S/GND

OCP/BD

R5［RO CP］

＋

－

LOGICLOGIC DRIVEDRIVE

Filter

RB1

RB2

Reg.V1

OCP

OCPM

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