AN3065 datasheet(20/33 Pages) STMICROELECTRONICS

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Test results and significant waveforms

AN3065

20/33

Doc ID 16279 Rev 2

4.4

Startup operation

On this demonstration board the startup resistors R7 and R16 charge C10 and C11 until the

L6563S turn-on voltage threshold is reached, at which point the L6563S starts switching.

Because once the turn-on threshold is reached the Vcc consumption increases and the

current supplied by R7 and R16 is lower, the L6563S is initially supplied by the Vcc

capacitor, and then the L1 auxiliary winding provides the voltage to supply the IC.

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 L6563S 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 L6563S 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

voltage exceeds a preset value (VOVP), usually larger than the maximum Vout that can be

expected, also including worst-case load/line transients.

Figure 27.

EVL6563S-100W TM PFC startup at

90 Vac, 60 Hz, full load

Figure 28.

EVL6563S-100W 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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