Circuit Analysis of the 1.8kW Induction Hotplate

Fig 6 – Simple Gate Driver



COOL THING #6 – Low drive requirement allows super simple 2-transistor driver!

Wow, a long list of really great stuff.  But alas, there is one pretty significant drawback when considering the use of this circuit for homebrew induction heating of metal: The work coil is “hot”.

Hot?  You ask.  Hot from awesome melting metal?

Yes, but also electrically hot.  Meaning that the massive (1kV) tank ringing is right on the wire of that work coil.  Touch it with the steel rod you’re trying to heat and you get killed – boo!  Whacking the work coil with the workpiece is one of the commonplace hazards of actual workingman’s induction heating.  You don’t want to do it, but it happens all the time.

So while this is a great piece of circuitry, we can’t say that it’s suitable for one of those cool levitation melting vids you see on YouTube.  Yet.

It’s probably possible to magnetically couple (through a ferrite toroid or other transformer core) this circuit to another work coil made from copper tubing, but we haven’t tried yet.  In that case, the dangerous voltages can all stay inside the protective case of the heater, and the work coil can happily run at a low voltage with an even HIGHER current.  Cool!

The trick there will be the impedance matching.  This circuit wants to run with a 50uH-ish inductance, and you don’t want a ton of turns on the primary side of the output transformer so a ferrite core may be tricky.  Air core?  Who knows.  We have a bunch of experiments lined up on our side, and we’d be happy to hear your suggestions on how to take this cheap and cheerful circuit from the kitchen to the forge.

Attached are our schematics in LTSpice format: Openschemes-Burton_Powerstage.  Just unzip everything into one folder, open the schematic (asc file) with LTSpice, and it should be ready to run.  We’ve included libraries (LIB files, they’re just text files with spice models) for the comparator, all the diodes, and the IGBT’s.  They will all unzip right where they need to be – right next to the asc file – so the simulator will automatically load them at sim time.

So go forth and tinker!  Please post here if you discover great things, cool mods, or build your own induction heater based on this design.  Once again, be careful and only take on projects you are qualified for – a dead ‘schemer is no good to anyone!  :)

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