L6564 STMicroelectronics, L6564 Datasheet - Page 24

• Manufacturer Part Number: L6564
• Description: 10 pin transition-mode PFC controller
• Manufacturer: STMicroelectronics

Application information
Figure 32. Effect of boost inductor saturation on the MOSFET current and detection method
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However, in some applications such as ac-dc adapters, where the PFC pre-regulator is
turned off at light load for energy saving reasons, even a well-designed boost inductor may
occasionally slightly saturate when the PFC stage is restarted because of a larger load
demand. This happens when the restart occurs at an unfavorable line voltage phase, i.e.
when the output voltage is significantly below the rectified peak voltage. As a result, in the
boost inductor the inrush current coming from the bridge rectifier adds up to the switched
current and, furthermore, there is little or no voltage available for demagnetization.
To cope with a saturated inductor, the L6564 is provided with a second comparator on the
current sense pin (CS, pin 4) that stops the IC if the voltage, normally limited within 1.1 V,
exceeds 1.7 V. After that, the IC will be attempted to restart by the internal starter circuitry;
the starter repetition time is twice the nominal value to guarantee lower stress for the
inductor and boost diode. Hence, the system safety will be considerably increased.
Doc ID 16202 Rev 4
L6564