limiting input voltage to LED driver ICs

[jmole]

I see that on a lot of linear LED drivers, they have a maximum LED Power supply voltage. On the surface, this makes sense, if you're controlling current with a MOS transistor. However, there are occasions where I'd like to use something like the TLC5940 to control 16 strings of LEDs, maybe with a supply voltage of 48V.

Datasheet: http://www.ti.com/lit/ds/symlink/tlc5940.pdf

I considered that maybe a Zener diode at the inputs would do the trick, but this is going to create a small current in the LEDs when they would otherwise be off, so isn't really the solution I'm looking for. Wondering if anyone else might have a clever solution.

There are certainly other chips out there, but I haven't found any that do individual PWM dimming on multiple channels of high-voltage LED strings.

[ajb]

The last time I was seriously looking at controlling a large number of LEDs I seem to recall seeing a number of multi-channel constant current drivers designed to be used with an external PWM signal, perhaps a setup like that would suit your needs?  The trick then is providing a sufficient number of PWM outputs.  If you only need 16 channels, you might be able to find a suitable micro with that many PWM outputs, or maybe an IO expander, or use the inverted output of the TLC5940, even.  If you need more channels something like the LT8500 (48 channels, with some nice control features) might be a better fit. 

If you can get away without the constant current drive, then of course you could simply use the TLC5940 to control an external transistor. 

Thinking a little more out of the box, if you can arrange your circuit so that the TLC5940's Vcc is at +48V (with it's ground at +43V), then you could use a current mirror to turn its output current around and drive your LEDs from the high side.  For higher currents that wouldn't be terribly efficient, though.