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Experimental Results
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14.1 Performance
In steady state, the LED string voltage is measured to be 21.55 V and the average LED current is
measured as 347.5 mA. The 100 Hz current ripple flowing through the LED string was measured to be
194 mA
pk-pk
at full load. The magnitude of the ripple is a function of the value of energy storage capacitors
connected across the output. The ripple current can be reduced by increasing the value of energy storage
capacitor or by increasing the LED string voltage.
The LED driver switching frequency is measured to be close to the specified 67 kHz. The circuit operates
with a constant duty cycle of 0.21 and consumes near 9W of input power. The driver steady state
performance for an LED string consisting of 6 series LEDs is summarized in the following table.
Table 1. Measured Efficiency and Line Regulation (6 LEDS)
V
IN
(V
RMS
) I
IN
(mA
RMS
) P
IN
(W) V
OUT
(V) I
LED
(mA) P
OUT
(W) Efficiency (%) Power Factor
180 30.65 5.42 20.59 219.40 4.52 83.3 0.9867
190 32.35 6.06 20.80 242.55 5.05 83.3 0.9869
200 34.21 6.75 21.00 267.37 5.62 83.2 0.9870
210 36.01 7.47 21.18 293.39 6.21 83.2 0.9871
220 37.74 8.20 21.37 320.18 6.84 83.3 0.9872
230 39.44 8.96 21.55 347.51 7.49 83.6 0.9873
240 41.22 9.76 21.72 375.52 8.15 83.6 0.9874
250 43..29 10.62 21.90 404.82 8.86 83.5 0.9875
260 45.06 11.57 22.07 436.75 9.64 83.3 0.9877
14.2 Current THD
The LED driver is able to achieve close to unity power factor (PF ~ 0.98) which meets Energy Star
requirements. This design also exhibits low current harmonics as a percentage of the fundamental current
(as shown in the following table) and therefore meets the requirements of the IEC 61000-3-2 Class-3
standard. Total harmonic distortion was measured to be less than 1.2%.
Table 2. Measured Harmonic Current
Harmonic Class C Limit (mA) Measured (mA)
2 0.78 0.022
3 11.61 0.125
5 3.90 0.11
7 2.73 0.105
9 1.95 0.11
11 1.73 0.15
13 1.73 0.093
15 1.73 0.071
17 1.73 0.154
19 1.73 0.165
21 1.73 0.065
23 1.73 0.065
25 1.73 0.08
27 1.73 0.084
29 1.73 0.065
31 1.73 0.07
14
AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver SNVA462F–November 2010–Revised May 2013
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