DN86

Issue 1 - October 2007

5

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© Zetex Semiconductors plc 2007

smoothed the ripple may drop below the combined LED forward voltage which stops the

switching regulator and so reduces the average current in the LEDs. This will also reduce the

average lumens output.

Figures 5 to 7 show the input voltage ripple and LX voltage varying the input capacitance value

and current precision. Reducing the input capacitance the output current precision will decrease

up to 25% with system efficiency always above 50%.

C1 [µF]

Vin [V]

Iin[A]

Vout[V]

Iout[A]

Efficiency

Current

Accuracy

100

12.70

0.303

9.28

0.225

54%

25%

150

12.60

0.394

9.50

0.271

52%

10%

200

12.53

0.432

9.55

0.293

52%

2%

300

12.50

0.386

9.70

0.295

60%

2%

Table 3 AC input voltage