I watched a Dave jones video on an energy harvester but I'm trying to figure out how the front end of this circuit actually resonates and how that steps up some small input voltage.
Is it a function of C2 and the inductance of the transformer?
Does the frequency that it resonates matter?
What powers the self resonating circuit?
Here is a screen shot of the circuit in question:
The Datasheet can be found here
Best Answer
It doesn't resonate - it's a step-up transformer (1:100). Each time the MOSFET switches on Vin gets transferred to the secondary with largely a 100:1 amplification in voltage just like a conventional transformer steps up or steps down (more usually) voltage.
ADDITIONAL INFO
Series resonation of the transformer's secondary leakage inductance and C2 cause the circuit to oscillate BUT, conceptually the MOSFET could be driven by an oscillator if one could be found to work at such low voltages.