I'm trying to control brightness of some commercially obtained instrument panels (for a mock aircraft cockpit). The panels have some internal LED strings (presumably, anyway) which are explicitly rated to a 2.8v input (and no more), and unfortunately must be switched on the high side. Maximum current draw I've measured on the bench is about 60-70mA.
I have an existing PWM module used for various other tasks in the system, which has spare outputs. The PWM chip on the module is a PCA9685 which can sink a decent amount of current, but 60-70mA is beyond what it can cope with.
Therefore my plan was to establish a 2.8v power rail using a small linear regulator, and use my PWM input through some kind of driver/switch to give the final 2.8v-PWM-ed signal to the backlight input. The problem is I can't find a suitable driver which works in the correct voltage range, but has a fast enough response time for PWM.
There's plenty of 'slow' solutions,(< 100 hz) even toggling the enable line of the 2.8v regulator, and there's plenty of fast solutions (designed for PWM) for automotive, but which need 12v output.
(I don't think I can use simple BJTs because of the junction voltage drop: below 2.8v the backlight is much less bright). In case it's relevant the PWM signal is at 5V.