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PQ1PF1

Primary Regulator for Switching Power Supply (50W Class)

Sharp Electronics 

Primary Regulators

PQ1PF1

s Description for Each Operation

1. Low voltage mulfunction prevention circuit

This device has a built-in low voltage malfunction prevention circuit to prevent malfuncting when power supply voltage Vcc

becomes as low as starting time. When power supply voltage comes up to operation starting voltageVCC( ON)17.0V TYP., IC will

start to operate. When power supply voltage falls short of operation stopping voltageVCC(OFF)9.3V TYP., IC will stop operating, and

output is shut down.

Before starting power supplies or after stopping operation, applying current to Vcc terminal is stood for stand-by current ICC(ST), and

it is kept at 100µA TYP. (Vcc=14V).

2. Oscillator

IC has a built-in oscillator, and oscillation frequncy is fixed at 100kHz TYP.

3. CA terminal

CA terminal can be connected to capacitor CA, and it enables to perform various functions such as soft start function, overcurrent

protection function, overvoltage protection function, and ON/OFF control function.

3-1 Soft start function

Soft start circuit is shown in Fig.1. When voltage Vcc is supplied, CA terminal voltage VCA starts rising, charging a capacitor CA

with charge current from CA terminal(10µA TYP.). According to rising CA teminal voltage VCA, output pulse width becomes

gradually wider, and it may cause soft start.

ON duty D of output pulse width is as follows.

D=0% at VCA=0.9V TYP.

D=Dmax=45% at VCA=1.8V TYP.

During normal operaion, VCA is clamped at 3.6V by the internal circuit of IC.

CA

CA 3 VCC 5

3.6V

←

10µA

OSC

+ PWM

FB

-

-

4

-

Fig.1 Soft Start Circuit

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