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I want to strobe a typical Chinese 100W LED chip on about a 20:1 ratio so that I only use a little over 5W of power. This is so a camera system can get a colour picture at night so a noticeable flashing isn't a problem.

I'm thinking of having a 33V PSU that charges a capacitor up and then this is discharged into the LED until the voltage drops enough to turn the LED off, whereby the cycle will repeat.

Has anyone flashed these LED chips and know what speeds they can be flashed at and still give full power ?

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  • \$\begingroup\$ Datasheet says? \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 24 '14 at 20:01
  • \$\begingroup\$ Little LED's will do 1 MHz easy. We've strobed 10W ones at low freq, but I don't know how fast one can go. I'm not sure I like your charged cap approach. How do you control the LED current? \$\endgroup\$ – George Herold Sep 24 '14 at 20:07
  • \$\begingroup\$ Have you thought about using a constant current driver? In my experience they lead to much better consistency and repeatability, especially across multiple PCBs. \$\endgroup\$ – Andreas Wallner Sep 24 '14 at 20:08
  • \$\begingroup\$ Nothing on the datasheet (typical Chinese produce :-) \$\endgroup\$ – Mike Bryant Sep 24 '14 at 20:22
  • \$\begingroup\$ The switch from the capacitor to the LED will limit the current a little. I've found most cheap PSUs can't take the load being turned on and off hence the thought of having the capacitor as a near constant load to the PSU. \$\endgroup\$ – Mike Bryant Sep 24 '14 at 20:24
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Nah, don't bother charging and discharging a cap like that. Just PWM it after the cap. The LEDs will be fine. Get a power supply of the right voltage, add a nice big cap at the output to reduce ripple in the power supply, then use a decent MOSFET transistor driven by some sort of PWM controller. Either high side or low side will work, but one may be a little more straightforward to implement. Generally low-side is easier to implement when you have to control something that runs at a higher voltage than the control logic. An Arduino could generate a PWM signal, or you could build something out of discrete logic or analog components (e.g. ramp generator and comparator). Doesn't really make too much difference.

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