I´ve made a circuit using a tlc5940 and a p-channel mosfet to control a 3W powerled. This is the circuit:
It works, but has one big problem: the dimming curve makes it more or less useless for my purposes of slowly fading in and out the light.
Two years ago I made a similar circuit based on the LM317 and a transistor, which worked quite ok, but which wasn´t very power-efficient and had the problem of the inverted output (4095 off, 0 on). This circuit made perfect fades though.
To illustrate, when using the p-ch mosfet circuit, changing from 1 to 2 (in the 4095 range) makes the light incredibly much brighter than 1. This would correspond to maybe about 50 steps using my old circuit.
I have tried with four different mosfets, giving more or less the same result (irf5305,irf9z24n,irf9510,irf9610).
So, is this an expected effect of using a p-channel mosfet or is there something I can do with my circuit to improve this?