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I'm an embedded software developer and am trying to up my electronics and board design knowledge. As a good first exercise I made a ZVS induction heater. project link

Once assembled I was happy to see that it worked! The oscillation is happening just fine and I can heat up metal. But when I cranked up the voltage to 8 volts or so (my initial tests were at 4-5 volts), one of my diodes let out the magic smoke. Apparently they're getting really hot!

Schematic

It concerns the D1 and D2 diodes. They are the UF4005, but I've also tried the FR107 (of which I know it was used in another similar design) with the same results.

So now the question is why these diodes get so hot.

I could probably blindly copy one of the designs on the internet, but then I wouldn't understand what is going wrong.

I measured the voltage across one of the diodes (at a system lower voltage) and got the following result. (Green is voltage across diode, yellow is voltage across the big inductor and capacitors)

Oscilloscope image

This voltage looks really weird. Why does it stay high for so long when the voltage across the inductor switches? This is the only thing I could probe that looks really weird.

The only thing I could find that could be wrong is the component choice for L1 and L2. Instead of winding my own coils I bought them. It seems that these inductors can get saturated. I don't know how I could measure that in this circuit, so I'm not sure if that's happening. But say that it does happen, then I can't see why that would overheat the diodes. I would just waste more power than necessary, right?

Anyways, these are the components that I think are relevant:

  • D1,D2: UF4005
  • Q1,Q2: NTP067N65S3H
  • C3,C4,C5,C6: MKS4O136806F00KYSD
  • L1,L2: 2300HT-221-V-RC

The zener diodes don't do anything yet because the voltage is still too low.

The oscillation happens at ~40khz.

As a reference, here's a schematic of the same concept in a different form:

Geoxion
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  • Any inductor with a magnetic core can saturate, whether you wind it yourself or buy it already wound. Are you able to measure any current waveforms? How high of a current is all this happening at--what current is going through the diodes that are getting hot? They're only rated for 1 A average, and only 2 W of power dissipation. – Hearth Dec 16 '22 at 15:15
  • @Hearth I haven't measured that because I would have to add in some resistor somewhere to measure it. In my simulation of the circuit these diode only carry a maximum current of 22mA and an average of ~8mA at 8V VCC. The chosen components cannot dissipate a lot of power because they aren't supposed to – Geoxion Dec 16 '22 at 15:23
  • Why not simulate the circuit and see if it's doing what you intended it to do. You can also measure power dissipated in a sim. It would also help if you drew the circuit more like the one you copied. Using net names for connections on analogue circuits becomes so tiresome on a circuit so puny. – Andy aka Dec 16 '22 at 15:24
  • How are you probing across the diode? Most scope probes are grounded, this will likely disturb the circuit. A differential measurement technique is required. – Tim Williams Dec 16 '22 at 15:48
  • *The chosen components cannot dissipate a lot of power because they aren't supposed to* Then why did your hot diodes release the magic smoke. Simulate it. – StainlessSteelRat Dec 16 '22 at 16:49
  • @StainlessSteelRat if you look at the sentence above the one you quoted, you'd see that I did simulate it. 22mA is the max current . These diodes have also worked in other people's projects, so I'm quite sure that it's not the diodes that are wrong here – Geoxion Dec 16 '22 at 17:19
  • I have tried with values of components. Nothing "weird" even at 24 V. Ok, current through the "load" is 400 A -> 15 A through the power supply (360 W). – Antonio51 Dec 17 '22 at 10:35

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