AN3106 datasheet(14/34 Pages) STMICROELECTRONICS

14 / 34 page

Functional check

AN3106

14/34

Doc ID 16775 Rev 2

Figure 20 the low-frequency ripple has been measured too. We note that the peak-to-peak

value is not very low because of the low output capacitances 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.

4.3

Dynamic load operation

The waveforms shown in Figure 21 and Figure 22 pertain to the demonstration board during

the operation of 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, the

dimming frequency has been chosen at 300 Hz, a typical value for dimming.

In Figure 21 the converter’s output current was 2.6 A and the dimming duty cycle was 90%,

thus very close to the converter’s nominal output power. The output voltage has two

modulations. One is due to the rejection of the PFC output voltage ripple already measured

in Figure 20 where the voltage variation due to the LED current dimming is superimposed.

The peak-to-peak variation is 5.37 V but it doesn't present any problem for the load since the

converters reject the modulation.

In Figure 22 instead the converter has been checked at light load, so the peak output

current was 3 A and the dimming duty cycle was 15%, for an output power of 21 W. Even in

this case, the peak-to peak modulation doesn't present any issue for the downstream

current regulators and the board still works correctly.

Figure 19.

EVL130W-STRLIG demonstration

board: high frequency ripple on

output voltage at 115 V - 60 Hz - full

load

Figure 20.

EVL130W-STRLIG demonstration

board: low frequency ripple on

output voltage at 115 V - 60 Hz - full

load

CH3: VOUT

AN3106 Datasheet(PDF) 14 Page - STMicroelectronics