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AN4376

PFC waveforms

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7

PFC waveforms

7.1

Input and output LED driver waveforms

The waveforms of the input current and drain voltage at the nominal input voltage mains and

nominal LED load are illustrated in this section. Drain voltage is modulated by the sinusoidal

shape of the input mains voltage and the peak increase with the line.

The input current is in phase with the input voltage and a high power factor is achieved

(PF > 0.9).

Also the LED current and output voltage have been checked.

Note that the regulated LED current remains constant all over the input mains voltage. The

LED pk-pk ripple is the ± 27% of the average current. Increasing the value of the output

capacitor it is possible to decrease the LED current ripple following (Equation 2 on page 9).

For this demonstration board 3 parallel capacitors of 68

F have been selected to have

a current ripple of less than 100 mA pk-pk with 23 LEDs each with a dynamic resistance

of 0.8

.

Figure 20. Input and output PFC waveforms

at 100 VAC - 50 Hz - PF = 0.9889

Figure 21. Input and output PFC waveforms

at 230 VAC - 50 Hz - PF = 0.9211

CH1: DRAIN

CH2: INPUT PFC CURRENT

CH3: VOUT

CH4: LED CURRENT

CH1: DRAIN

CH2: INPUT PFC CURRENT

CH3: VOUT

CH4: LED CURRENT