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Registered Member #4860
Joined: Fri May 11 2012, 04:42PM
Location:
Posts: 13
Hi all,
I've just built my first ZVS. It worked great for a few minutes, producing 6-7cm arcs at 24V (far better and hotter than the 555 driver did on the same flyback). After a few minutes, while drawing an arc, both the FETs went bang. It was sequential, one went immediately followed by the other.
They both have big craters just above the source pin. The heatsink was barely warm.
Initially I though that perhaps the capacitor (a 0.68uF 400V MKT) had gone open-circuit, causing the failure. But the capacitor tests fine.
My only other suspicion is that I had the inductor too close to the flyback (around 3cm away), which resulted in the toroid saturating. Could that have been it?
Any other ideas on what may have caused the failure?
Registered Member #4860
Joined: Fri May 11 2012, 04:42PM
Location:
Posts: 13
Wolfram wrote ...
We need more info about your setup. What sort of core is the inductor wound on?
Hi Wolfram,
The inductor is wound around a 1 inch ferrite ring. It has 20 windings of PVC insulated multi-strand (32/0.2mm, 1mm2 conductor area), and measures at 150uH. I would have used 16 gauge enamelled copper wire, but I don't have any to hand.
The rest of the circuit is exactly as per the standard Mazilli circuit.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
The basic circuit is unsafe, even if well built. If for some reason, as excessive load (arcs), core saturation (arcs), etc. the oscillation stops, it self-destructs immediately. Something added to limit the input current (at least a fuse) or the output load (series resistor) may extend the life of the circuit for some time.
Registered Member #4860
Joined: Fri May 11 2012, 04:42PM
Location:
Posts: 13
Antonio wrote ...
The basic circuit is unsafe, even if well built. If for some reason, as excessive load (arcs), core saturation (arcs), etc. the oscillation stops, it self-destructs immediately. Something added to limit the input current (at least a fuse) or the output load (series resistor) may extend the life of the circuit for some time.
So is it common for the FETs to explode? Do other people running this circuit experience this?
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Yes; the ZVS driver has issues with exploding if something causes one of the transistors to latch on...it then steals all of the current from the other mosfet, and then explodes from overcurrent.
The other mosfet will then explode after.
Why? If you look at the way the circuit feedback is designed, and the way the gate driving is, you'll notice that if you didn't have the resonant circuit there, the mosfets would be on. Completely and utterly on.
So if for any reason the resonant circuit stops oscillating or "leaves" the circuit the mosfets will explode from overcurrent.
Registered Member #4860
Joined: Fri May 11 2012, 04:42PM
Location:
Posts: 13
:-)
Ok, I get it, you don't like the ZVS. But you have to admit, it is very elegant (up until it explodes). The arcs I got off it were way hotter than anything I've seen with my 555 driven FET.
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ZVS IRFP250 catastrophic failure
