PQ1PF1 查看數據表（PDF） - Sharp Electronics

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PQ1PF1

Primary Regulator for Switching Power Supply (50W Class)

Sharp Electronics 

Primary Regulators

PQ1PF1

3-2 Overcurrent protection function

Overcurrent protection circuit is shown in Fig.2. Fig.3 shows timing chart of OFF control process after detecting overcurrent.

First, drain current of MOS-FET (which is built-in device) is getting high due to overcurrent. When it comes up to overcurrent

detection level ID(OCP)=2.5A, overcurrent protection circuit will operate and minimize output pulse width to minimum duty by pulse-

by-pulse. Minimizing output pulse width makes output voltage lower. As output voltage is lowered, collector-emitter voltage of

PC1 will be turned OFF and FB voltage VFB will be high. When VFB comes up to threshold voltage of overload shut-down VFB(OCP)

2.8V, CA voltage VCA will be released from clamped voltage 3.6V and the capacitor CA which is connected to CA terminal will be

charged again by 10µA of charge current. When VCA increases to CA threshold voltageVCA (OVP) 7.7V, internal constant voltage

supply of IC becomes OFF-state and maintain shut-down state. To maintain output shut-down condition, 0.3mA (Vcc=11V) TYP.

is required. To restart, Vcc needs to be lowered less then operation stopping voltageVCC(OFF) 9.3V by applying input voltage again.

Fig.2 Overcurrent Protection Circuit

CA

35

1

4

PC1

PQ1PF1

2

Fig.3 Timing Chart Overcurrent Protection

Output current

VFB

VFB (OCP)

2.8V

VCA

3.6V

VCA (OVP)

7.7V

DMAX

DMIN

0

Overcurrent Overload shut-down

detection

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