STR-A6359 データシートの表示（PDF） - Sanken Electric co.,ltd.

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STR-A6359

Hybrid IC with a built-in power MOSFET and a controller IC

Sanken Electric co.,ltd. 

STR-A6300 Application Notes

≒5V

発振器電圧

≒0V

≒0.76V

C5両端電圧

≒0V

STR-A6300

OSC

ﾌｫﾄﾄﾗﾝｼﾞｽﾀによる直流ﾊﾞｲｱｽ

発振器出力 ON OFF ON

0

MOSFET

DC bias by

photo -transistor

PWM Latch

SQ

R

OCP.Comp

Vth(1)

+

‐

Reg1

Drive

（Ver.1.2）

PC

⑦⑧D

R2

①S VR4

④OCP/FB

②⑤Gnd

R4

C5

R5

VR5

Fig.7 Oscillati図n7g 定O電p圧er制a御tio時nのa発t振c動on作stant voltage control

Feedback current (FB current) through a photo-coupler flows to R4, and the voltage drop VR4 is added to

VR5. That is, the VR4 (FB current) controls the VR5 voltage (peak ID) which requires to reverse the OCP

Comp., and the output is controlled in the current mode.

Generally, in the current mode control, the bias from VR4 increases at light mode, and the OCP Comp. shall

be functioned faultily by the noise caused from the surge current at the MOSFET turn-ON. In order to avoid

this problem, the impedance between the OCP/FB (No.5) and the GND terminal is reduced by an

Active-Low-Pass Filter Circuit while the MOSFET is turned OFF.

The Active-Low-Pass Filter circuit is composed of the 0.8mA constant current by-pass circuit between the

OCP/FB (No.5) and the GND terminal, and it reduces the bias by 50% until the MOSFET is turned ON.

This function enables C5 to absorb surge noise when the MOSFET is turned ON and achieves a stable

control at light load.

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