- on Power Supplies
- Published in issue 7/2006 on page 0
Driver for 20 LEDs
If we wish to use a step-up switching regulator to run several LEDs from, for example, a 3 V battery, we find that the maximum usable mark-space ratio limits us to driving just a few LEDs in series. If we have seven white LEDs in series the total forward voltage will be about 7 times 3.4 V, or 23.8 V, requiring a mark-space ratio of around 90 %. This is the upper limit for many switching regulators.