Question about a flyback's polarity


I am confused with this flyback transformer I have.
I have a pulsed DC input on the primary coil (pulses from 0 to 15V) and that creates high voltage in the secondary coil.

When I connect that input in the opposite direction (wrong polarity) I don't get high voltage any more.
The possible explanation for this is that the primary coil has a diode in series with it.

Now, I'm confused by this because I tested if there actually Was a diode in there (by connecting a DC supply and a DC motor, in series with the coil) and the motor always works!
(also tested with a halogen light)

I put the coil in series with the motor to test if there is a diode inside. If there would be one inside, the motor should not work in one of the two cases, when I switch the pins of the primary coil.

So, as the results of the test tell me: there is no diode in series with the primary coil.

could it be possible that there is a diode in parallel with the primary coil?
If that's not possible, how come the flyback is not working when I connect the polarity incorrectly?

Could someone please help me out with this?



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There's often a diode in the SECONDARY
I don't live on IRC - if you see Lizzyastro on there, try pinging her.

The "instructable" is a work in progress - no pictures.



Would you like to see my unfinished notes on FLyback action ?
iceng5 years ago
Yea that's the case Lol
No we don't because we switch it off pretty quick, or we WILL saturate the core.

iceng5 years ago
Still much fun,
But really the varnish on a small pulsed transformer for residential use must dampen mechanical and magnetostrictive events not just quiet but silent..

The varnish does the job and has a low visible acrid stink if burned.that can
permeate a room..  Avoiding this smelly possibility the fly black transformer
is over designed which explains why they are a favorite among hobbyists .
DC in a transformer will NOT have no effect - it will cause the core to saturate. You MUST NOT have standing current in the transformer.
Or acrid smoke will rise up and smite thy lodgings.