LTspice 12V SMPS flyback transformer ?

[lordvader88]

I made my 1st 1/2 of a 12V SMPS, using values from 1 whose bulk cap blew up, and blew the plastic case/glue apart.

So I have the EMI stage, the single nmos, an inductor standing in as 1/2 the flyback. And I made a pnp multi-vibrator to stand in for the PWM chip.

And it works 1st try !! Making circuits is fun.

So what's the easy way to make a flyback transformer in LTspice that will output about 12.7V @1A ?

[Buriedcode]

I'm not sure I fully understand.  You made an actual circuit, that blew up?

You mention you want a 12V output, but what is the input voltage? Mains? 48V ? 6v?

A flyback is essentially a boost converter, with a coupled inductor (an inductor with more than one winding). If you're just playing around with an inductor, NMOS and multi-vibrator I'm not sure you fully understand how a flyback converter works.  Start here: https://www.dos4ever.com/flyback/flyback.html

It is an excellent article explaining how the converter works, and why we select the parts and values we do.  LTspice is also very handy for testing ideas, but the values (inductance, saturation current, DC resistance etc..) for a transformer will vary depending on the application, its not really about output voltage - strictly speaking it isn't really a transformer, because in a flyback converter it stores energy. It isn't like a mains AC transformer that has a rated output voltage for a given input voltage.

[lordvader88]

I have a real SMPS that blew up. And I had drawn the circuit ages ago, so I put it in spice. It runs from sine wave 169V 60Hz, I'm using the resistor and cap values from the real SMPS. So I made the hot side, but I need a flyback transformer model.

[mvs]

I need a flyback transformer model.

Put two inductors (L1 and L2) on your schematic and couple them using SPICE directive K1 L1 L2 1

[Buriedcode]

I have a real SMPS that blew up. And I had drawn the circuit ages ago, so I put it in spice. It runs from sine wave 169V 60Hz, I'm using the resistor and cap values from the real SMPS. So I made the hot side, but I need a flyback transformer model.

Start with a boost converter.  I'm aware this will step up voltage, but once you have a boost converter, you can add a second winding to the inductor in LTspice as indicated by mvs above.  The turns ratio of the inductors is the square of the inductance. So if you want a 10:1 ratio, then primary should have 100 times the inductance of the secondary.  The feedback comes from this secondary winding.

[lordvader88]

ok thanks