# Another question about LEDs in series

I have been doing a lot of reading on trying to match constant current drivers to series of LEDs but either my calculations are incorrect or the demands of what I am proposing are way off the charts. This is part of a project to make a strobe light.

I would like to run 5 LEDs in series, here are the specs of each individual LED:

wattage:20w | foward voltage:30-32v | forward current:700ma

The ideal would be a driver with a fair amount of leeway, so that I could work with fewer or more LEDs, depending on the situation.

I know that all the questions on this topic must be driving you guys crazy, but there is so much contradictory information online, and it is hard to calculate with any confidence. So, if someone could tell me exactly what I need from a driver, I would be very grateful.

• are you in the US? if so, that's going to be difficult to do, since you need ~150v to drive those in series. is the strobe duty cycle <50%? if so, you can "cheat" the requirements by half. Dec 30, 2017 at 19:56
• You need a rather high voltage so you'd better be careful! Not only during development but also to have a safe housing to put it in. Dec 30, 2017 at 20:09
• The forward voltage of a white LED is somewhere around 3 or 4V. That means that what you are dealing with is an LED string. Just FYI. Meanwell has a module that would work. For example the HVGC-150-700. meanwell.com/webapp/product/search.aspx?prod=hvgc-150 Dec 30, 2017 at 20:12
• meanwell can be a good choice but maybe not for a strobe. A DIY supply with no concept of thermal issues or cascading voltages is MM... Dec 30, 2017 at 20:16
• @PaulClift I'm not sure how you're planning on fitting several hundred 20ms pulses into each second. Once you hit 50, the LED will be constantly on. Dec 30, 2017 at 22:54

If you have 5 LEDs in series, and each should be run at 700mA, then you need to deliver a current of 700mA.

If each LED develops 30v to 32v voltage drop at that current, then your current source must tolerate delivering into a total voltage drop of 150v to 160v.

5 30V 700mA leds in series? That's 150V at 700mA. So you need a constant current supply that can do that much. If you want to use less leds, it needs to be able to do 120V, or how ever lower voltage * leds you remove. If you want to add more, then the same applies. Add 30V for each led that you are adding.

So if you want to use 4 to 6 leds, thats a range of 120V to 180V. Good luck.

• Hmm, following your (and other users' on here) advice, I think that individual drivers for each LED is the way to go on a project like this. That way, I will be dealing with more manageable voltages and it will simplify running heat-sink fan from the same power source... Dec 31, 2017 at 12:51