On Fri, Jan 30, 2015 at 3:54 AM, Jesse Lackey w= rote: > Beware this calculation is at 25deg C, and the question of "how hot will > it get?" is not straightforward to answer. > > Look up "temperature rise in FETs" from december 22 2014 for a thread > about it. Good tip, I forgot about that threat already! > In my use - highspeed PWM for LED drivers, I'm doing a design at this > very moment to get 2600 steps at 24Khz - the switching speed wasn't the > problem. (I'm using a gate driver FWIW.) 100% is the worst case for > heat, driving the gate at 9V. > > Also Josh - camera flicker is going to depend on the camera and the > settings, how much other light there is, and the power supplies used. I > sell a 32-channel DMX dimmer designed to have no flicker on camera, and > the rates required has varied from customer to customer. 1800 Hz has > been fine (Metropolitan opera in NYC making a DVD of a performance), and > other times 7.2Khz was needed (a variety of movies and TV studios). You > will also possibly have to contend with audible noise from your circuit > or the power supply when switching significant current in the audible ran= ge. > > Hence the 24Khz in the latest new design. > > If you'd rather buy than build drop me a line for details. I am familiar with your excellent work! In this particular instance I am doing a few less standard things with the user interface, so I wasn't able to just buy modules. That had been my first plan...before the feature creep! I believe you use an SO8 FET, right? Do you find any issues with heat there? I definitely won't be putting things as dense as you have. As a side question, how did you deal with generating all the channels of PWM? Are you doing it all in software on the processor, or do you have some kind of PWM specific chip? Thanks! Josh --=20 A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .