STR-A6351 Ver la hoja de datos (PDF) - Sanken Electric co.,ltd.
Número de pieza
componentes Descripción
Fabricante
STR-A6351 Datasheet PDF : 17 Pages
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STR-A6300 Application Notes
（Ver.1.2）
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 ID flowing to R5. The
voltage has a saw-tooth waveform as that of the ID, and almost the same voltage as VR5 is imposed on the
No.4 terminal. When the No. 4 terminal voltage reaches the threshold voltage Vth(1)≒0.76V, OCP Comp.
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.
When both-ends-of-the capacitor voltage rises up to around 5V, the oscillator output is reversed again and
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 (ID) becomes ON-time of the MOSFET. Furthermore, the fixed
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
Oscillation voltage
≒5V
発振器電圧
≒0V
≒0.76V
C5両端電圧
≒0V
発振器出力 ON OFF ON
0
MOSFET
STR-A6300
OSC
=>C5 voltage
=>Oscillator
Output
PWM Latch
SQ
R
OCPComp.
Vth(1)
+
‐
Reg1
Drive
⑦⑧D
①S
④OCP/FB C5
②⑤Gnd
R5
Fig.6 Oscillation O図p6 eSrWa電t源io構n成o時fのS発w振i動tc作h-Mode Power Supply
Page 10
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