Electrical waveform

AN4346

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DocID025107 Rev 1

3

Electrical waveform

3.1

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.

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:

Equation 2

For this demonstration 3 parallel capacitors of 330

F have been selected to have a current

ripple of 250 mA pk-pk with 7 LEDs each with a dynamic resistance of 0.8



Figure 24. Input and output LED driver

waveforms at 100 Vac - 50 Hz

Figure 25. Input and output LED driver

waveforms at 230 Vac - 50 Hz

CH1: DRAIN pin

CH2: INPUT CURRENT

CH4: LED CURRENT

CH1: DRAIN pin

CH2: INPUT CURRENT

CH4: LED CURRENT



14

f

l







2

+

-----------------------------------------------------------------------

2455mA



14

 50Hz R

LEDtot

3330

F













2

+

-----------------------------------------------------------------------------------------------------------------

=

