Flyback converter reflected voltage

[hithesh123]

I am trying to understand when exactly the voltage is reflected from secondary to primary in a flyback converter.

1. The Switch turns ON, the primary inductor current ramps up
2. The switch turns OFF, current is induced in the secondary inductor-->diode conducts -->capacitor charges
3. The switch turns ON again and the secondary voltage is reflected to the primary side???

 

[RCinFLA]

Flyback transformer is better described as a coupled inductor. Energy is stored in magnetic field, charged by primary, discharged by secondary.

A regular power transformer tightly couples primary to secondary and minimizes energy stored in core.

 

[mtwieg]

The secondary voltage is always reflected to the primary (and vice versa).

 

[electrophysics]

I am trying to understand when exactly the voltage is reflected from secondary to primary in a flyback converter.

1. The Switch turns ON, the primary inductor current ramps up
2. The switch turns OFF, current is induced in the secondary inductor-->diode conducts -->capacitor charges
3. The switch turns ON again and the secondary voltage is reflected to the primary side???

it is no. 2 i.e. when switch turns off. the first voltage which develop on primary is its own Vdc input supply voltage. this voltage is added with Vo * n where n is turns ratio and Vo is output voltage. another voltage which is also added to primary in off condition is due to primary and secondary leakage inductance and should be clipped in proper way using snubber or zener clamp.

 

[hithesh123]

it is no. 2 i.e. when switch turns off. the first voltage which develop on primary is its own Vdc input supply voltage. this voltage is added with Vo * n where n is turns ratio and Vo is output voltage. another voltage which is also added to primary in off condition is due to primary and secondary leakage inductance and should be clipped in proper way using snubber or zener clamp.

How is it no. 2?
The switch turns OFF, there is nowhere for the mag flux to go other than the secondary winding.
The secondary windind is conducting until cap voltage is equal to induced voltage (vo). Now the diode stops conducting, the stored energy has to go somewhere. It's reflected to the primary?

 

[ea.arun]

my understanding is when the secondary winding is conducting(that its charging the output capacitor through the diode) primary is not connected to the main power since main switch is off........during that time the transformer configuration is as a normal one(not like when the primary switch was conducting and there is no secondary current flowing due to the diode reverse bias and so there is no connection b/n primary and secondary winding).....so it will couple back to the primary as a normal transformer....
thats why we will select the primary zener values(above main supply+Reflected) which will not impede the secondary and reduce the effective power delivered or eficiency......