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I'm planning to build a multi-zone outdoor lighting system, controlled by an Arduino. This will be a 12v DC system, and use purchased 12v DC landscape lighting.

I plan to control each 'zone' with a simple MOSFET switch and use the Arduio's PWM outputs to enable independent dimming of the zones - one PWM output per zone.

My question is about power supply selection. Ideally, I'd like to get a single power supply rated to handle all of the lights in the system, say 120W. However, I am unsure how to select a power supply that will allow for PWM dimming on the 12v side of the circuit.

I am currently looking at : http://ca.mouser.com/ProductDetail/Mean-Well/HLG-120H-12/?qs=3IPTn0w%2f0t%252bZhU8K7VADrQ%3d%3d

can you help me determine how to tell if a power supply is suitable for the purpose I've described?

the other option is to use several smaller 'dimmable' power supplies (one per zone) and run the PWM signal directly into them.

Thanks,

Adam

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  • \$\begingroup\$ Why are you unsure - what form does this doubt take? \$\endgroup\$
    – Andy aka
    Dec 29, 2015 at 23:46
  • \$\begingroup\$ I'm primarily unsure if the power supply will be able to 'keep' up with the PWM switching. If, for example, I have a single set of lights at 40% duty interval, then the power supply will be going from no load to load very rapidly - I sadly don't know enough about power supplies to understand from the data sheet if this is OK given a specific supply. \$\endgroup\$ Dec 30, 2015 at 11:36

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I'm primarily unsure if the power supply will be able to 'keep' up with the PWM switching. If, for example, I have a single set of lights at 40% duty interval, then the power supply will be going from no load to load very rapidly - I sadly don't know enough about power supplies to understand from the data sheet if this is OK given a specific supply.

Virtually any simple to complex voltage power supply will be able to satisfy your doubts. Generally speaking, the output of a power supply will be a large reservoir capacitor and this component will "soak up" the current impulses taken by a load. Imagine it like a large flywheel on a rotating engine - it has the mass (and energy storage) to cope with large changes in load without slowing down the engine driving the flywheel.

Another thing to consider is that most modern power supplies will be based around switching converters so they are dealing with large and rapid changes in current and voltage due to the switching transistors anyway.

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A quick and dirty method is to add the wattage of all the LEDs you plan to use, and double this. The find a power supply with the power and voltage meeting your spec.

Also consider future expansion - if you think you might add additional zones in the future, add those to the total now, so you don't run into a problem later.

Also over design your wire gauges by at least 100%, that way you can safely tap a new zone off of an existing one (within reason).

Also - I honestly think your design will be simpler if you have just a single supply, with a separate dimmable (PWM) circuit. Because you're using PWM to dim your lights, it uses less power as the current is switched off for a period of time. But you have to factor in the possibility that all lights are on full brightness.

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I suggest you driving LED's with series connection and adding a low-power, high voltage step-up converter to convert from, for example 12V to 120V DC for the series LED's.

To calculate needed voltage, take the Vfd from the diode and multiply by number of diodes.

A good circuit to use is the MC34063 to step the voltage up. It will fit to 50 LED's of Vfd's at 2V.

24V input is optimal for the MC34063 and 50 LED's, as a step-up factor of 6+ is hard to make stable.

Good luck!

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