Oscillator circuit operation in smps.

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ArivNidunami

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I am new in smps. I only want to understand how this circuit oscillating, especially the function of aux winding. Thanks.
 
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I'll take a shot at it. When power is applied, current flow through R2 & R3 into the base of T1 starts to turn it on. The collector of T1 goes low and current flows in the transformer primary winding. The aux winding is phased such that feedback through C2 turns T1 on harder. When the transformer saturates, the feedback collapses and the junction of R2/R3 is driven negative, turning T1 off. After the transformer field totally collapses, T1 is again turned partially on via the current from the supply through R2/R3 and the cycle repeats.
 

Thank you for your response. I draw a current flow with it, but i'm not sure.
Can you re-draw it? I know it will take more work, i really appreciate it. Thanks.
 
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Loosely applied oscillation requires positive feedback and a gain of 1.
This is provided by the aux winding C2 and R3.
The operation is not unlike a blocking oscillator.
 
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