Multiphase LED Driver

check LTC3731.

This what you mean?

Mark L. Fergerson

I don't think that explains what an "Multiphase LED" driver is ??!!

What is a "Multiphase LED" driver ?

hamilton

Well I'm guessing it has the same meaning for switching power supplies as an LED driver can be buck, boost or buck-boost:

I can only imagine the OP wants to have a high powered LED driver that can respond rapidly to large changes in current.

Mark.

Why would you do a multi-phase LED driver? ...and why boost?

What's changing the current?

I've no idea, it doesn't sound like a 'normal' LED driver. However, high powered IR LEDs could be used for data transmission, or laser LEDs. Anything that pulses the LEDs on and off quickly would require a fast response. As for boost, maybe its a battery application with multiple LEDs and best way is to put them in series. Just guessing.

Mark.

There still is nothing external varying the current. If the idea was to linearize a transfer function, I'd expect feedback into the driver. I still see no need for multiple phases. Sure, LED drivers may look like buck regulators but that doesn't mean what makes sense for a regulator works for a LED driver. BTW, I realize you're not the OP.

Ok, I get your point on boost. I suppose it could be for single-cell batteries driving blue LEDs, too. Point taken.

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Do they ever use the LED as the 'diode' in a switch mode supply or just as the load? (Sorry, perhaps a silly question, but I remember looking at siwtch mode circuit topologies one night and wondering...)

George H.

We don't know that. If the LED was turned off by an enable signal to the driver, then turned back on again, the response to turning on would be faster with a multi-phasic architecture (each inductor is smaller that a single one, current ramps up more quickly - that's one of the advantages).

You're right, it's not the norm for LED drivers. There are other advantages I can see though. If it's high powered it may require a physically large inductor. Having somewhat several smaller inductors might mean you can build the circuit with a lower height profile, and the heat might be spread out over a wider area. We won't know until the OP responds!

I'd think not. They're pretty lossy. ;-) LEDs aslo suck in the reverse direction.

But the driver is doing the switching. That's sorta the point.

I don't see how multiple phases are going to do anything a higher frequency wouldn't do. I haven't thought this through completely, though.

Perhaps "Power Boy" (the OP) simply was perusing the marketing literature for his new PC motherboard* and is wondering if the same technology as used there would make sense for a power LED load. I don't think it would for a typical illumination application- neither very low output ripple nor voltage agility are particularly important for that kind of an LED.

Eg.

Best regards, Spehro Pefhany

I'm talking about modulating the output of a driver to form an on/off light source. The rate you can do that will depend on the effective frequency of the switcher (switching LED drivers generally have a PWM or enable signal to do this). When the driver is turned on the response time will depend on effective switching frequency, so a multiphasic driver could respond much faster and therefore be modulated faster.

Generally speaking this would be true, however what happens when you reach the switching frequency limit for a driver? The only way to get an effective higher frequency is by phasing multiple inductors. There's also the question of EMI, four inductors running out of phase each running at a quarter of the effective switching frequency will produce less higher order harmonics.