Driver question/idea

Flashlight Modding and DIY Parts
1

I was looking into the different driver models: buck/boost, linear (AMC7135)
My results:

- linear regulator should suck (since they drop the voltage by burning it off) but are quite good because the voltage of a single cell is close to the one needed (3.7v - 3.4V)

  • buck converter should be better but you loose too much energy in converting it

so my question is why not simply put in a mosfet and regulate the output with pwm to max. 3.4-3.5V?
does the resistance of the led change that much when it gets hot?

2

I realized i made a stupid mistake :8)
I can’t measure the output voltage with the controller ADC since it measures the input relative to supply so there is no way of knowing how many volts there are absolutely.

so i need a way of measuring the absolute voltage, or how about a hall-effect current sensor to measure the current actually going to the led?

3

Yes the Vf changes as the led heats and is variable with each individual led. This is why we use current controlled drivers instead voltage regulators