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FAN7930C Datasheet(PDF) 12 Page - ON Semiconductor |
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FAN7930C Datasheet(HTML) 12 Page - ON Semiconductor |
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12 / 22 page  www.onsemi.com 12 PFC operation VCC VSTART VSTOP 5V VINV(=VPFCOUT) 2.240V 2.051V VRDY 2.500V t PFC operation VCC VSTART VSTOP 5V VINV(=VPFCOUT) 2.240V 2.051V VRDY 2.500V t Figure 25. Tw o Cases of RDY Triggered HIGH PFC operation VCC VSTART VSTOP 5V VINV(=VPFCOUT) 2.240V 2.051V VRDY 2.500V t PFC operation VCC VSTART VSTOP 5V VINV(=VPFCOUT) 2.240V 2.051V VRDY 2.500V t Figure 26. Tw o Cases of RDY Triggered LOW 4. Control Range Com pensation: On time is controlled by the output voltage compensator w ith FAN7930 C. Due to this w hen input voltage is high and load is light, control range becomes narrow compared to w hen input voltage is low . That control range decrease is inversely proportional to the double square of the input voltage ( ). Thus at high line, unw anted burst operation easily happens at light load and audible noise may be generated from the boost inductor or inductor at input filter. Different from the other converters, burst operation in PFC block is not needed because the PFC block itself is nor mally disabled dur ing standby mode. To reduce unw anted burst operation at light load, an internal control range compensation function is implemented and show s no burst operation until 5% load at high line. 5. Zero-Current Detection: Zero-current detection (ZCD) generates the turn-on signal of the MOSFET w hen the boost inductor current reaches zero using an auxiliary w inding coupled w ith the inductor. When the pow er sw itch turns on, negative voltage is induced at the auxiliary w inding due to the opposite w inding direction (see Equation 1). Positive voltage is induced (see Equation 2) w hen the pow er sw itch turns off. AC IND AUX AUX V T T V (1) AC PFCOUT IND AUX AUX V V T T V (2) w here: VAUX is the auxiliary w inding voltage; TIND is boost inductor turns; TIND auxiliary w inding turns; VAC is input voltage for PFC converter; and VOUT_PFC is output voltage from the PFC converter. PFC Inductor Aux Winding VIN PFC VOUT PFC ZCD VTH(ZCD) + - VCC THD optimized Sawtooth Generator Restart Timer gate driver RZCD CZCD Negative Clamp Circuit Positive Clamp Circuit 5 S Q R Q fMAX limit optional Figure 27. Circuit Near ZCD Because aux iliary w inding voltage can sw ing from negativ e to positive voltage, the inter nal bloc k in Z CD pin has both pos itiv e and negative voltage c lamping circuits. When the auxiliary voltage is negative, an internal circuit clamps the negativ e voltage at the Z CD pin ar ound 0.65 V by sourcing current to the serial resistor betw een the Z CD pin and the auxiliary w inding. When the auxiliary voltage is higher than 6.5 V, current is sinked through a resistor from the auxiliary w inding to the ZCD pin. |
Similar Part No. - FAN7930C |
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Similar Description - FAN7930C |
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