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I have an 100W constant current LED driver that I bought in error but maybe I can use it in another way. I want to use 3 buck regulators to pwm control each individual color of 90W RGB LED. Can I input constant current supply to a buck regulator (will use 30W max per channel)?

Constant current driver is rated as 8~12V while buck regulator is rated at 9-48V, will this cause any issues especially when PWM is used?

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  • \$\begingroup\$ Circuit diagram and component specifications essential. | What is LEd voltage - one LED/colour or N in series. .. \$\endgroup\$ – Russell McMahon Jan 26 '14 at 11:38
  • \$\begingroup\$ Voltage of the LED is completely irrelevant. I am asking if the regulator can work with constant current and not if it can work with the LED. \$\endgroup\$ – DominicM Jan 26 '14 at 14:25
  • \$\begingroup\$ "Completely irrelevant" may just marginally exist in an engineers toolkit but should be locked away for emergency use only. Note that I asked 'one LED ... or N in series". If > one LED per string then knowing how many is relevant. We do not know what you know, and assuming you mean xxx when you do not can and does lead to bad answers. \$\endgroup\$ – Russell McMahon Jan 26 '14 at 21:02
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You can't force a constant current into a buck regulator. Think about it. Where would the extra power not used by the final load go?

So this question is really about what the constant current supply will do under low load, and if that is something the buck regulator can handle. What does the constant current supply do when open? If it goes to its maximum output voltage, and the voltage is less than the 48 V the buck regulator can handle, then all should be fine. If it shuts down or occasionally retries with pulses, then it won't work.

As often, the solution is to read the datasheets.

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  • \$\begingroup\$ Thanks, that makes sense. As for datasheets, I would if they existed for cheap Chinese parts :) \$\endgroup\$ – DominicM Jan 26 '14 at 14:27
  • \$\begingroup\$ @Dominic: Then don't buy cheap Chinese parts without datasheets when you need this level of information. It sounds like you got what you paid for, even though without a datasheet I don't see how you can even know what exactly you did pay for. \$\endgroup\$ – Olin Lathrop Jan 26 '14 at 14:56
  • \$\begingroup\$ The only other option is to buy a brand name product pre-built product and forego DIY. It's either cheap or nothing. \$\endgroup\$ – DominicM Jan 26 '14 at 18:49
  • \$\begingroup\$ @DominicM - CCP's, not always, but often enough, use ICs of known brand with markings intact. You can often get a reasonable idea of what made up devices are potentially capable of by examining the components. IC types, inductor sizes, capacitor capacitance and voltage rating. 105C caps (tells you mainly about the mindset of the designer), MOSFET etc types, ... \$\endgroup\$ – Russell McMahon Jan 26 '14 at 21:06
  • \$\begingroup\$ Yes, if you are an engineer or have electronics background that might work but for everyone else it's just not plausible. Point is there are no datasheets most of the time and components can often be sealed in waterproof casing not that it matters as this question was very general. \$\endgroup\$ – DominicM Jan 26 '14 at 23:51

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