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Saturatable Reactor + ZVS driver?

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LAN_403

Thomas W

Sun Aug 28 2011, 12:46PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
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Posts: 1276

Hi 4hv,
do you think its possible to use a saturatable reactor for the inductor for a ZVS driver and would it be any use?

thanks,
Tom Williamson

Dr. Dark Current

Mon Aug 29 2011, 12:05PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I think it is not possible, you need a core which does not saturate - an iron powder or gapped ferrite.

Antonio

Mon Aug 29 2011, 12:52PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

I think that much of the frequent destructions of this kind of oscillator are due to core saturation or excessive loading, or both. It enters an alternative oscillation mode that draws much more current and destroys the transistors. Actually, it's so easy to change to this mode that I would not consider this circuit for any purpose requiring a minimum of reliability.

Ash Small

Mon Aug 29 2011, 01:41PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Am I correct in thinking that a saturable reactor could be used in series with a capacitor and primary of an H-bridge to maintain a fixed frequency at different loads? (some feedback would be required)

Or am I on the wrong track?

Proud Mary

Mon Aug 29 2011, 02:13PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Tom, there's nowt special about the inductor in the ZVS design. It's just an ordinary choke of 100Î¼H or so - like this one here on fleabay:

And it's easy enough to wind them yourself.

Thomas W

Mon Aug 29 2011, 03:59PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
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Posts: 1276

i know,
i just thought it could be interesting if you used it like a saturatable reactor to change what the inductor changes XD

Inducktion

Mon Aug 29 2011, 05:38PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Antonio wrote ...

I think that much of the frequent destructions of this kind of oscillator are due to core saturation or excessive loading, or both. It enters an alternative oscillation mode that draws much more current and destroys the transistors. Actually, it's so easy to change to this mode that I would not consider this circuit for any purpose requiring a minimum of reliability.

What do you mean alternative oscillation mode?.... What happens to the waveform, and what would happen if you used a semiconductor that can handle that sort of load?

Proud Mary

Mon Aug 29 2011, 06:50PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Inducktion wrote ...

What do you mean alternative oscillation mode?.... What happens to the waveform, and what would happen if you used a semiconductor that can handle that sort of load?

There's an obvious risk of parasitic oscillation and instability if the power supply choke ceases to have a sufficient choking action (due to saturation) and so becomes part of the frequency-determining LC circuit.

I agree with Antonio that this is a badly designed circuit. There isn't even any decoupling between the choke and the power supply, any open invitation for instability.

Antonio

Mon Aug 29 2011, 08:00PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Inducktion wrote ...

What do you mean alternative oscillation mode?.... What happens to the waveform, and what would happen if you used a semiconductor that can handle that sort of load?

This is a simulation of a typical ZVS, showing what happens with the input current if the choke inductance is reduced below a certain critical value. In this case it works correctly with 67 uH, but enters a destructive mode with 66 uH:

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