AN3105

Functional check

Doc ID 16774 Rev 2

13/30

On the lefthand side of Figure 9 the high frequency ripple has been measured; as seen the

ripple and noise at switching frequency is very limited, thanks to the low EMI generated by

both stages. On the righthand side of Figure 9 the low frequency ripple has also been

measured. It is possible to note that the peak-to-peak value is not so low but it doesn't affect

the application, in fact the converters regulating the current flowing in each LED strip can

reject the ripple without any problem.

Figure 9.

EVL130W-SL-EU demonstration board: high and low frequency ripple on output

voltage at 230 V - 50 Hz - full load

4.3

Dynamic load operation

Waveforms reported in Figure 10 are relevant to the demonstration board during operation,

supplying converters dedicated to power LED strips with constant current.

In both figures it is possible to see the output voltage modulation during operation with

variable load due to the dimming of the LED current by PWM. For both measurements,

a dimming frequency of 300 Hz has been chosen.

On the lefthand side of Figure 10 the converter output current was 2.6 A and dimming duty

cycle was 90%, therefore very close to the converter nominal output power. The output

voltage in the image has two modulations; one is due to the rejection of the PFC output

voltage ripple already measured in Figure 9, on the righthand side. Over imposed there is

the voltage variation due to the LED current dimming. The peak-to-peak variation is 5.37 V,

this doesn't create any problems for the load as the converters reject the modulation.

Whereas on the righthand side of Figure 10 the converter has been checked at light load, so

the peak output current was 3 A and dimming duty cycle was 15%, for an output power of

21 W. Even in this case the peak-to-peak modulation doesn't give any trouble to the down-

stream current regulators and the board still works correctly.

CH1: HB voltage