Flyback transformer action
Posted by: powerfly
on
I am trying to understand the flyback action -
Here's what I understand -
Let Vin =100V DC & turns ratio be 10:1 (pri:sec) and Vout = 5V
When the TOP switch is ON, the Voltage on the primary is Vin=100V. The voltage on secondary is 100/10 = -10V.
So when the switch goes OFF, this -10V is reversed and it should be +10V. correct?
How does this become 5V?
The most confusing part is -
When exactly is the reflected voltage transferred to the primary.
Voltage is reflected to the primary first and then the polarity at the secondary reverses? or do they happen simultaneously.
Comments
Thanks. Is there an application note or article that describes the VOR, polarity reversal with waveforms?
No I don't think we have a formal app note
When the switch turns off the primary side voltage begins to rise. The secondary does not begin to conduct until the primary side voltage reaches about VOR. This is the time that the secondary diode starts conducting and the current starts flowing into the output capacitor and load.
The polarity reversal happens instantaneously. It is only related to di/dt. So the instant the primary switch turns off di/dt becomes negative and the polarity reversal occurs.