STR-A6351 SanKen, STR-A6351 Datasheet - Page 10

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

When both-ends-of-the capacitor voltage rises up to around 5V, the oscillator output is reversed again and
STR-A6300 Application Notes
Fig.6 shows how the oscillator works when the IC operates without the constant voltage control.
The built-in capacitor is discharged and the value becomes around 0V when the MOSFET is ON. Besides,
the voltage drop (VR5) occurs at the OCP/FB terminal (Pin 4) by the drain current I
voltage has a saw-tooth waveform as that of the I
No.4 terminal. When the No. 4 terminal voltage reaches the threshold voltage V
starts its operation, and the MOSFET shall be turned OFF by reversing the comparator of the internal
oscillator.
The capacitor starts charging when the MOSFET is turned OFF, and the capacitor starts charging through
the constant current charging circuit, and both-ends-of-the capacitor voltage starts rising in accordance with
the gradient determined by the capacitor and the constant current charging circuit.
the MOSFET is turned ON, and the capacitor is discharged to around 0V rapidly.
The MOSFET continues the oscillation by repeating this cycle.
The time determined by the gradient of VR5 (I
time determined by the capacitor and the constant current charging circuit is OFF-time of the MOSFET.
This fixed time is adjusted at approximately 15usec by the constant current charging circuit
C5両端電圧
発振器出力
発振器電圧
≒0.76V
≒5V
≒0V
≒0V
MOSFET
Oscillation voltage
0
ON
OFF
Fig.6 Oscillation Operation of Switch-Mode Power Supply
ON
STR-A6300
=>C5 voltage
=>Oscillator
Output
図6 SW電源構成時の発振動作
OSC
D
) becomes ON-time of the MOSFET. Furthermore, the fixed
Page 10
D
, and almost the same voltage as VR5 is imposed on the
PWM Latch
S
R
OCP
Comp.
Q
+
‐
Vth(1)
Drive
Reg1
th
(1)≒0.76V, OCP Comp.
D
flowing to R5. The
④OCP/FB
（Ver.1.2）
②⑤Gnd
⑦⑧D
①S
C5
R5