Hi everyone,

I am just trying to understand how this smps circuit work that showed below. In circuit, there are 2 resistor which is 750k to start up. But I can not figure out that how transistor on and off. Before off period the current flow on R1 and R2 the transistor on and after that auxilary windding charge up C1 ? And there is R6 to limit primary current on the winding. Also I think the circuit has voltage feedback using diode and R5(56ohm). That's all I got from this circuit. Can anybody help about to understand deeply?

 

It's called a blocking oscillator.
Read this for some info on how it works.
Google has more references.