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[on:]

I have some older Luxeon high power LEDs and bought some drivers (spec below) to power them. They work fine for what I need.


However, I am going to be controlling these using TIP120 circuits (one to one) from an Arduino and it occurs to me that I don't know if I should be controlling power flow to the driver or to the lamp itself. I'll be doing both on/off and PWM.

Might sound like (and be..) a dumb question but when I stopped to think of it I wondered about which is least stressing on the hardware, delayed start and/or hysteresis. Is there a best practice or rule of thumb here?

[Reply #1 on:]

The drivers are no doubt constant-current drivers - this means their output terminal will rise to whatever voltage will yield that current through the LED or LED-string.  This voltage is not very well defined (depends on power supply voltage, LEDs, temperature...)

So I'd suggest using the darlington transistor to switch power to the driver (low-side switching), since then we know the voltages will be what we want (emitter at ground, base via resistor to Arduino pin, collector to negative supply to driver...

[Reply #2 on:]

These drivers don't necessarily react well to having their outputs switched off. They rely on the power consumption of the LED to stabilize the circuit -- you'll notice they frequently specify the number/wattage of the LEDs they are designed for.

I'd suggest digging around the DX site and reading the forum posts regarding dimming techniques for similar drivers.

[Reply #3 on:]

Thanks for the replies!

Good point about destabilizing the circuit - makes sense now that you point it out.

[Reply #4 on:]

I'm not suggesting switching off the driver outputs, but switching off the whole driver circuit low-side.  Much easier.