User manual

Experimental Results
The LED driver is designed to accurately emulate an incan-
descent light bulb and therefore behave as an emulated
resistor. The resistor value is determined based on the LED
string configuration and the desired output power. The circuit
then operates in open-loop, with a fixed duty cycle based on
a constant on-time and constant off-time that is set by select-
ing appropriate circuit components. Like an incandescent
lamp, the driver is compatible with both forward and reverse
phase dimmers.
NON-DIMMING PERFORMANCE
In steady state, the LED string voltage is measured to be 20.5
V and the average LED current is measured as 350 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 port and the TRIAC firing angle.
The ripple current can be reduced by increasing the value of
energy storage capacitor or by increasing the LED string volt-
age. With TRIAC dimmers, the ripple magnitude is directly
proportional to the input power and therefore reduces at lower
LED current.
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 8.75 W of input power.
The driver steady state performance for an LED string con-
sisting of 6 series LEDs without using a triac dimmer is
summarized in the following table.
MEASURED EFFICIENCY AND LINE REGULATION (6 LEDS, NO TRIAC DIMMER)
V
IN
(V
RMS
) I
IN
(mA
RMS
) P
IN
(W) V
OUT
(V) I
LED
(mA) P
OUT
(W) Efficiency (%) Power Factor
180 31.73 5.35 19.67 221.64 4.36 81.4 0.9375
190 33.39 5.96 19.85 244.82 4.86 81.5 0.9394
200 35.11 6.61 20.04 269.16 5.39 81.6 0.9493
210 36.85 7.30 20.22 294.82 5.96 81.6 0.9493
220 38.53 8.01 20.40 321.26 6.55 81.8 0.9451
230 40.18 8.75 20.56 348.70 7.17 82.0 0.9463
240 41.75 9.50 20.74 375.70 7.79 82.0 0.9477
250 43..39 10.30 20.90 404.82 8.46 82.1 0.9490
260 45.07 11.14 21.05 434.48 9.15 82.0 0.9500
DIMMING PERFORMANCE
The LED driver is capable of matching or exceeding the dim-
ming performance of an incandescent lamp. Using a simple
rotary TRIAC dimmer, smooth and near logarithmic dimming
performance is achieved. By varying the firing angle of the
TRIAC dimmer and measuring the corresponding input and
output parameters, the dimming performance of the demon-
stration board driving 6 LEDs is summarized in the table
below.
MEASURED DIMMING PERFORMANCE
V
IN
(V
RMS
) V
O
(V) I
LED
(mA) P
OUT
(W)
229.39 20.51 343.1 7.04
220.47 20.35 320.8 6.53
210.24 20.16 294.8 5.94
199.05 19.98 266.8 5.33
190.32 19.80 245.8 4.87
180.33 19.61 222.7 4.37
170.51 19.42 200.1 3.89
156.39 19.31 187.4 3.62
149.11 19.15 171.6 3.29
140.35 18.97 154.0 2.92
129.61 18.75 133.1 2.50
119.7 18.53 115.3 2.14
110.17 18.33 99.1 1.82
100.55 18.11 83.5 1.51
90.75 17.87 68.8 1.23
79.72 17.59 53.1 0.93
70.42 17.34 40.8 0.71
60.91 17.08 30.1 0.81
49.94 16.77 19.8 0.33
45.04 16.64 16.0 0.27
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