AN2941 datasheet(21/37 Pages) STMICROELECTRONICS

21 / 37 page

AN2941

Functional check

Doc ID 15447 Rev 4

21/37

HV startup circuit turns on and begins to operate periodically in order to keep VCC between

VCCON and VCCON-0.5 V (Figure 21) maintaining the IC latched.

If R37 is shorted, the impedance externally connected to pin #15 (VFF) is lower and the

voltage in case of OVP cannot reach the 5+2VBE threshold, so the L6566A restarts after

VCC has dropped below 5 V (Figure 22). In case of L6566A OVP intervention, the L6563S

operation is also stopped because the L6566A stops the PFC via the Vcc_PFC pin.

Additionally, to improve the immunity against temporary disturbances (needed for example

in case of immunity tests), an internal logic activates the protection after the OVP has been

detected for 4 consecutive switching cycles.

Figure 20.

Flyback open loop at 230 V-50 Hz

half load

Figure 21.

Flyback open loop at 230 V-50 Hz

half load

CH1: VFF voltage

CH2: Vcc

CH3: ZCD voltage

CH4: Output voltage

CH1: VFF voltage

CH2: Vcc

CH3: ZCD voltage

CH4: Output voltage

Figure 22.

Flyback open loop - restart option 230 Vac 50 Hz - half load

CH1: VFF voltage

CH2: Vcc

CH3: ZCD voltage

CH4: Output voltage

AN2941 Datasheet(PDF) 21 Page - STMicroelectronics