STR-A6351 SanKen, STR-A6351 Datasheet - Page 11

• Manufacturer Part Number: STR-A6351
• Description: STR-A6300 Series
• Manufacturer: SanKen

Generally, in the current mode control, the bias from VR4 increases at light mode, and the OCP Comp. shall
STR-A6300 Application Notes
C5両端電圧
発振器出力
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 I
Comp., and the output is controlled in the current mode.
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.
発振器電圧
≒0.76V
≒5V
≒0V
≒0V
MOSFET
0
ON
OFF
ﾌｫﾄﾄﾗﾝｼﾞｽﾀによる直流ﾊﾞｲｱｽ
ON
Fig.7 Oscillating Operation at constant voltage control
STR-A6300
DC bias by
photo -transistor
図7 定電圧制御時の発振動作
OSC
Page 11
PWM Latch
OCP.Comp
S
R
Q
+
‐
Vth(1)
D
) which requires to reverse the OCP
Drive
Reg1
④OCP/FB
（Ver.1.2）
②⑤Gnd
⑦⑧D
①S
VR5
C5
R2
VR4
R4
R5
PC