NCP1072STAT3G(2012) 查看數據表（PDF） - ON Semiconductor

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NCP1072STAT3G
(Rev.:2012)

High-Voltage Switcher for Low Power Offline SMPS

ON Semiconductor 

NCP1072, NCP1075

APPLICATION INFORMATION

Startup Sequence

When the power supply is first powered from the mains

outlet, the internal current source (typically 8.0 mA) is

biased and charges up the VCC capacitor from the drain pin.

Once the voltage on this VCC capacitor reaches the VCC(on)

level (typically 8.2 V), the current source turns off and

pulses are delivered by the output stage: the circuit is awake

and activates the power MOSFET if the bulk voltage is

above VHV(EN) level (91 V typically). Figure 21 details the

simplified internal circuitry.

Vbulk

I1

Rlimit

ICC1

1

Istart1

I2

CVCC

Iclamp

-+

Vclamp = 8.4 V VCC(on)

VCC(min)

Iclamp > 6 mA ?

--> OVP fault

Drain

5

8

Figure 21. The Internal Arrangement of the Start−up Circuitry

Being loaded by the circuit consumption, the voltage on

the VCC capacitor goes down. When VCC is below VCC(min)

level (6.8 V typically), it activates the internal current source

to bring VCC toward VCC(on) level and stops again: a cycle

takes place whose low frequency depends on the VCC

capacitor and the IC consumption. A 1.4 V ripple takes place

on the VCC pin whose average value equals (VCC(on) +

VCC(min))/2. Figure 22 portrays a typical operation of the

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