AN2811

Test results and waveforms

Doc ID 14904 Rev 1

13/25

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Test results and waveforms

Figure 10 shows the overall efficiency versus a range of AC line voltage loads with one LED

and two LEDs. Under both load conditions, we can observe that the efficiency drops when

input voltage increases. The maximum efficiency occurs at minimum AC line input

(176 VAC). Comparing a load condition of one LED with a load condition of two LEDs in

series, the efficiency increases by 7%. The efficiency with 1 LED is close to 75%.

Figure 10.

Efficiency versus input voltage

Figure 11 shows us the standby power which is measured when the LED is disconnected.

Standby does not mean burst mode under light load. In standby, the overvoltage protection

works. Under various AC line inputs, the maximum standby power is 0.18 W at 264 V input.

Figure 11.

Standby power versus input voltage

With the aid of the filter formed by C11, L2 and C3, no high-frequency interference can be

observed at the input current which definitely helps in meeting the conducted EMI standard.

In Figure 12 and Figure 13 the waveform is captured at 176 VAC. In Figure 14 and Figure 15

the waveform is captured at 264 VAC.

To choose the proper rating of the fuse, we always refer to the inrush current. There are two

inrush current plots at the AC line input 220 V: Figure 16 with one LED and Figure 17 with

two LEDs.