> In your application, I think I'd just try to come up with a constant +24V > supply. You may be able to do this with a charge pump converter. I've use= d > one from TI that could output something like 300mA, but I think it will b= e > difficult finding a charge pump chip that will do much power at 24V. So, > you're probably back to a boost converter. Linear Technology has some nic= e > simple boost converter chips, and maybe even some modules that have > everything in one assembly. I think such a single chip solution will be > simpler than trying to build your own charge pump. If this a one off / some off / high volume application? The circuit that I described using semi-pseudo-SPICE-code is in fact a voltage doubling (almost) charge pump. As I described it it drives the LED string via an external current setting resistor. But, short R1, add a reservoir cap C2 at the output and one more diode (location left as an exercise for the student but clue: it stops the pump capacitor C1 from back charging from C2 when Q2 is turned on. You now have an ~=3D 24V supply and can current regulate the LED to control brightness and "flashing. The above stats allow resistor value and The converter needs a square wave of probably asymmetric mark space, but a square wave would do. Having no overlap on the two FET gates is a very good idea (tm) but a complete driver could be achieved with ed CD40106 or equivalent, glue parts as above plus a few more glue bits for the oscillator. HOWEVER - we have allowed the discussion to mislead us away from what is actually wanted (or some of us have :-) ). Aim is to provide extra brightness and the 24V figure provided is a "probably good enough" voltage but limits the result achievable. Josh should ideally tell us more. At least, what is I_LED at 12V and 24V and how many LEDs of what colour (white?). LED part numbers would help. Is the resistor value known. If 12->24 doubles current then with the above information we can have a reasonable idea of the resistor value (if not already known or knowable). Using a "normal" SMPS/Boost converter with current feedback will allow the LEDs to be flashed or held at any desired brightness with ease. ___________ I don't think you say how many LEDs are in the string. I_LEDs =3D (Vin =3D (N x V_LED))/R VLED ~~~~ constant. 4 LEDs is marginal to dead on 12V. 3 LEDS allows about 3V max drop across R at 12V so about 15 at 24 V so I_LEDs increases by about 5:1 !!! @ LESDs allows about 6V drop at 12V and 18V at 24V or about 3:1 I_LED ratio= .. IF the LEDs are operated at << Imax at 12V then all may be well. If I_LED at 12V ~> Imax_optg then the above suggests "there will be trouble= ". 3:1 on bright is at Cree max limit and 5:1 is above it. Duty cycle is about 7:1 so Cree suggestion is well violated if LEDs are run at max voltage and there are 3+ LEDs in string. More data will help tie down the above guesstimates. Russell --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .