AN3119 datasheet(19/32 Pages) STMICROELECTRONICS

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AN3119

Test results and significant waveforms

Doc ID 16849 Rev 2

19/32

4.4

Startup operation

Figure 29 and 30 show the waveforms during the startup of the circuit at mains plug-in.

The R5 and R11 startup resistors charge the Vcc C9 capacitor, therefore Vcc voltage rises

up to the turn-on threshold, and the L6563S starts operating. For a short time the energy is

supplied by the Vcc capacitor, and then the auxiliary winding with the charge pump circuit

takes over.

Because the startup resistors are always connected to the mains, their power consumption

during normal operation might affect the efficiency of the power supply once it operates at

light load. Therefore the value of the startup resistors must be found as a compromise

between the startup time at minimum input mains and the power dissipation at maximum

input mains.

In Figure 28 and 29 the waveforms during startup of the circuit at mains plug-in are shown.

Notice that because the Vcc voltage rise depends on the input voltage, the wake-up time is

dependent on the input mains voltage.

The same figures show that the output voltage rises from the peak value of the rectified

mains to the nominal value of the PFC output voltage and the good phase margin of the

compensation network allows a clean startup without overshoot.

Figure 29.

EVL6563S-250W TM PFC: startup at

90 Vac-60 Hz - full load

Figure 30.

EVL6563S-250W TM PFC: startup at

265 Vac-50 Hz - full load

CH1: PFC output voltage

CH2: Vcc voltage (pin #14)

CH3: RUN (pin #10)

CH4: gate drive (pin #13)

CH1: PFC output voltage

CH2: Vcc voltage (pin #14)

CH3: RUN (pin #10)

CH4: gate drive (pin #13)

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