Produce 60V AC (25Hz) from a 6V battery - will this work?

[Odysseas]

Alright. I'll try installing the freewheeling diodes and see if they turn to smoke or if the current consumption of the entire circuit rises significantly.

 

[alec_t]

Hmm. Another sim shows circulating current through the diodes. I don't know which one to believe

 

[Odysseas]

I imagine some current is to be expected, the question is how much and where it comes from.

 

[ericgibbs]

Hmm. Another sim shows circulating current through the diodes. I don't know which one to believe

hi alec,

Rerun your 60V25Hz.asc using a 'real' diode types rather than the idealised LTS model.

Eric

 

[Odysseas]

I tried installing the diodes. They didn't blow up in my face, but the current consumption rose quite considerably. It was about 50mA before, and about 150mA after installing the diodes. The next thing for me will be to increase the PWM frequency. 10 kHz is a nice place to start I think.

 

[alec_t]

Rerun your 60V25Hz.asc using a 'real' diode types rather than the idealised LTS model.

Did that (thanks, Eric). A more believable result, showing significant recirculation current in the freewheel diodes. Ran the sim again without the diodes and was surprised to find they are probably unnecessary (at least when using the guessed inductor values I used), as the kick-back voltage on the twin input windings is only ~ 50% above the supply voltage. Strange things, magnetics

 

[Odysseas]

Sorry this took so long, a Raspberry Pi happened to pass my way and I couldn't resist. My efforts to get a decent sine wave out of my transformer have been met with limited success. I have increased the PWM frequency to 8 kHz and this is what I get out of the transformers primary windings (I haven't increased the number of values in the sine lookup table.)

My knowledge of magnetics is somewhat limited. Anybody have any idea what is going wrong here?

 

[tcmtech]

More importantly what does your secondary side look like and what does it look like with a bit of capacitance added to it to make it work more like a LC tank circuit of sorts?

 

[Odysseas]

More importantly what does your secondary side look like and what does it look like with a bit of capacitance added to it to make it work more like a LC tank circuit of sorts?

Please note, by secondary side I mean the one which is actually labelled 'secondary'. In my application I actually feed current into the secondary side, of course.

I have made a snapshot of both PWM signals which control the two MOSFETs. I have also fed one of these signals through an RC low pass filter (100n, 100k) and recorded the waveform there as well.

 

[tcmtech]

Okay. The other secondary side.

To me a transformer is a transformer and the terms primary and secondary relate to which windings are getting the power put in and which are sending power out.

 

[Mr RB]

...
My knowledge of magnetics is somewhat limited. Anybody have any idea what is going wrong here?

Yes, your PWM frequency is 1kHz, which is much too low. The transformer does not filter out 1kHz very well, so it is appearing as nasty 1kHz noise on the transformer output.

Try increasing PWM freq to 10kHz or better still 20kHz.

 

[Odysseas]

It's ringing I have changed the PWM frequency to 8kHz and simply tried connecting a phone bell to the transformer output - and voila! Admittedly, the output waveform is not exactly a clean sine wave but it does the job.

Thanks a lot, mates!

 

[Mr RB]

Congrats!