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Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
I think the screech is pretty typical. The arc is changing the load and bringing the frequency down into the audible range. I'm sure someone else can describe the reason a little better than i can at the moment (3am.) I've noticed the same thing happening every time i stretch a zvs arc out.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I think it's the circuit jumping into another oscillation mode, which is not optimal. To eliminate it you may try increasing the Q of the circuit by increasing the air gap in the core and the resonant capacitor. This might, however, result in the primary/core dissipation going up too much.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The sound you describe is due to kinetic energy generated in the 'flyback' core as it expands and contracts at the frequency of the alternating current. This effect is called magnetostriction and is one of the properties associated with ferromagnetism.
It is the reason that 50/60 Hz power transformers hum at 50/60 Hz, and why overloaded transformers hum ever more loudly as the overload is increased.
Magnetostriction is sometimes used to generate ultrasonic pressure waves for parts cleaning, and in high power marine echo location devices. The familar ping of Second World War submarine ASDIC - sonar - was produced by magnetostrictive transducers.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
I was experimenting with a homemade transformer last night with the ZVS for my new capacitor bank charger and at first I forgot to connect the resonant capacitor to the primary coil.
The circuit seemed to work but it made a nasty screeching noise without it.
Perhaps it would be a problem with your capacitor?
Registered Member #4118
Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140
The choke in a ZVS has constant current going through it. Iron powder works for constant current, but not for ac (you couldn't make a flyback core out of iron powder). Ferrite works for both, but saturates at a much lower current than iron powder, so it's easier to use iron powder for a cc inductor.
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ZVS flyback driver making a screech sound
