AN44 ZETEX [Zetex Semiconductors], AN44 Datasheet
AN44
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AN44 Summary of contents
Page 1
... AN44 A high power LED driver for low voltage halogen replacement Introduction LED lighting is becoming more popular as a replacement technology for Halogen low voltage lighting, primarily because of the low efficiency, reliability and lifetime issues associated with Halogen bulbs. Discussed below is a novel approach for driving high power LED replacement for low voltage halogen lighting systems ...
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... AN44 So T can be calculated, as the voltage across L1 is obtained by subtracting the forward LED ON voltage drop from V . Therefore smaller and the same battery voltage V PEAK I , the current is flowing through the LED and so the average current in the LED is the sum of PEAK ...
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... Note that, for an LED drop of 9.6V and a Schottky drop of 300mV, the time to ramp down from 680mA to zero would be: 680mAx22µH TDIS --------------------------------------- = 1.5µ 9.6 + 0.3 Issue 2 - July 2006 © Zetex Semiconductors plc 2006 Figure AN44 , then the device MIN and I MIN PEAK www.zetex.com ...
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... AN44 As the T period is nominally 1.7µs, the current should have time to reach zero. However, 1.5µs OFF is rather close to 1.7µs and it is possible that, over component tolerances, the coil current will not reach zero, but this is not a big issue as the remaining current will be small. Note that, because of the peak current measurement and switch-off not possible to get the dangerous ‘ ...
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... Typical performance graphs for 24V system Figure 5 Performance graphs for 24V system Issue 2 - July 2006 © Zetex Semiconductors plc 2006 5 AN44 www.zetex.com ...
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... AN44 Useful formulae for calculations The input power from the battery during TON (assuming discontinuous operation mode /2. The average input current from the battery is therefore this current multiplied by the ratio PEAK the total cycle time PEAK ON × ...