I had a 555 timer-based PWM generator lying around for another project but I noticed it flickered on camera so I made some tweaks to the circuit and increased the frequency from 1kHz to about 30kHz, hopefully, there won't be any flicker, if there is then its just a simple change of a capacitor.
I don't expect the ring to get very hot but in case it does, I made the ring as dense as possible with copper and exposed the copper on the backside.
For the dimmer PCB, I just made the timer circuit as small as possible, I'll be using micro USB to power the ring light and the microscope and I shouldn't see any issues with current consumption from the USB power supply.
The ring is estimated to take 720mA at full brightness, ill be running each LED at 50mA instead of 60mA, which will keep it cooler as well.
White solder mask on the ring is to prevent any colour distortion.
The PCB's are on the way as well as the components. I also bought a stencil with the led ring, first time using one so will be interesting. I also bought an MHP30 by MiniWare but just realised that the heating plate is too small :), may need to do it in sections or something.
The next update will be when everything arrives and I can start to assemble, haven't tested anything except the 555 timer circuit so hopefully the LED ring is ok.