AN3063 datasheet(20/33 Pages) STMICROELECTRONICS

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Test results and significant waveforms

AN3063

20/33

Doc ID 16261 Rev 3

4.4

Startup operation

On the L6563H, the high-voltage startup function is implemented. The HVS (pin #9), is

directly connected to the DC bulk voltage and at startup, an internal high-voltage current

source charges C10 and C11 until the L6563H turn-on voltage threshold is reached, at

which point the high-voltage current source is automatically switched off. As the L6563H

starts switching it will be initially supplied by the VCC capacitor, and then the transformer

auxiliary winding will provide the voltage to power the IC. Because the L6563H integrated

HV startup circuit is turned off, it is not dissipative during normal operation. It has a

significant role in reducing power consumption when the power supply operates at light

load.

In the following

Figure 27 and 28 the waveforms during the startup of the circuit at mains

plug-in are shown. We can notice that the Vcc voltage rises up to the turn-on threshold, and

the L6563H starts operating. As mentioned previously, for a short time the energy is

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

takes over. At the same time, the output voltage rises from the peak value of the rectified

mains to the nominal value of the PFC output voltage. The good margin of the

compensation network allows a clean startup, without any large overshoot.

4.5

PFC_OK pin and feedback failure (open loop) protection

During normal operation, the voltage control loop provides for the output voltage (Vout) of

the PFC pre-regulator close to its nominal value, set by the resistor ratio of the feedback

output divider. In the L6563H the PFC_OK pin has been dedicated to monitor the output

voltage with a separate resistor divider composed of R3, R6, R11 (high) and R15 (low), see

Figure 2. This divider is selected so that the voltage at the pin reaches 2.5 V if the output

Figure 27.

EVL6563H-100W startup at 90 Vac,

60 Hz, full load

Figure 28.

EVL6533H-100W startup at 265 Vac,

50 Hz, full load

CH1: PFC Output voltage

CH2: Vcc voltage (pin #16)

CH3: RUN (pin #12)

CH4: Gate drive (p in #15)

CH1: PFC output voltage

CH2: Vcc voltage (pin #16)

CH3: RUN (pin #12)

CH4: Gate drive (pin #15)

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