Here I have a switching power supply diagram that I found on the internet. I have a slightly different one for which I would like to adopt this same scheme for starting process so that I can keep the control circuit completely isolated from the input, but I can't understand how this works.
The auxiliary source, which comes out of the secondary of the toroidal transformer, is responsible for powering the control circuit. At the moment the source is turned on, there is no energy in the secondary, so when turning on the source, the control circuit theoretically should not work and the PSU shoudn't start. I imagine that when turning on the source, as the primary is energized, the circuit does something to induce a sufficient current in the secondary to start the IC.
What I want to know is how this happens.