Ringing choke converter basic question

[ku637]

Hi,

Im trying to learn the working of a ringing choke converter, so did a basic simulation in LTspice.

[Sorry i can't post an image as usual here.. but an screenshot link is attached.Sorry for the inconvenience]


<iframe src="https://www.screenr.com/embed/AKLN" width="650" height="396" frameborder="0"></iframe>

https://www.screenr.com/AKLN



I suppose Q1 turns ON through the startup resistor 15k.But once turned ON, the L2 will get a voltage induced on it in the same polarity as L1.This can send current into the base node aiding turning ON process to be faster. But how the transistor turns OFF.??

In the Graph Wave Forms -Legend from Top to Bottom

1.Inductor current
2.Vce
3.Vbe
4.Vout at capacitor

Thanks for any help,

 

[D.A.(Tony)Stewart]

The forward conduction of secondary pulse current is inverted phase to the transistor base current pulse.

 

[BradtheRad]

I believe this is a similar principle to a blocking oscillator. Also used in the 'joule thief' converter.

R1 carries current, biasing the transistor on.

Current through L1 builds.

Eventually it is at a sufficient level so that L2 conducts. This turns off the transistor. It turns off current in L1.

The cycle starts all over.

 

[chuckey]

" Current through L1 builds.", so the voltage across L2 is a constant ( V = L X DI/DT). When the current STOPs increasing, i.e. DI/DT goes negative, the voltage across L2 changes polarity and switches the transistor off.
Frank