Half-Bridge Inverter (Induction Heater) - Page 1
Forum section: electronics / projects

author: JimStephens
author_rank: Newbie
timestamp: March 08, 2015, 04:23:32 pm
content: Hi all,I am in the process of building an induction heater using a half bridge inverter. Square wave (50 VDC / 2) switching at the resonant frequency.I have a couple of questions and I would also welcome anyone's advice/opinion on what I can do to improve the circuit and to confirm that my circuit is going to work as expected.PSPICE Simulation results for output current show 9 A RMS, ~200WComponents:Optoisolator: 4N25http://www.vishay.com/docs/83725/4n25.pdfIGBT: SGL 160N60UFDhttp://pdf.datasheetcatalog.com/datasheet/fairchild/SGL160N60UFD.pdfHalf-Bridge Driver: IRS2183http://datasheet.eeworld.com.cn/pdf/IRF/152736_IRS2183.pdfMicro controller: ArduinoMy questionsI am powering the half-bridge driver (IRS2183) from an external 15 VDC Supply. This same supply will power the optoisolator (4N25). This is ok to do and wont cause me any issues will it?I am using 2k pots on the IGBT gates - this a good approach?I am using 22nF caps on the circuit driver (Vcc-Vss, Vb-Vs, Com-Vcc)I would like to add snubber capacitors to the switches but I have yet to look into the design of that yet.I hope to design a little PCB soon I so would appreciate peoples advice on the circuit.Sorry for the rough drawingThanks,JS

author: bktemp
author_rank: Super Contributor
timestamp: March 08, 2015, 06:56:31 pm
content: Quote from: JimStephens on March 08, 2015, 04:23:32 pm4N25 is too slow. Better use a fast logic optocoupler like 6N137.QuoteMuch too large. Gate resistors are in the range of 5-50ohms.QuoteA bit low. 100nF-1uF are typical valuesAt 50V mosfets are probably a better choice than IGBTs because of their lower RDSon and faster switching time.

author: Seekonk
author_rank: Super Contributor
timestamp: March 08, 2015, 07:06:09 pm
content: Melting cans or cooking lunch? Couple years back I was looking at some melting sites. Got a solar powered camp and I have 50V raw from the panels. I should build an induction cooktop and save some propane. Why opto isolator at all? Doesn't look line operated. Waiting to hear more.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 08, 2015, 08:33:45 pm
content: Those IGBTs are MONSTERS! Way too big for this. With gate resistors as large as that, they'll switch... oh about the time the glaciers finish melting?Necessities: current transformer or other sensor; output voltage (coil / caps) sensor, phase detector (usually using the current transformer), variable frequency controller (e.g., combining the PD and VCO by using a CD4046), overload, undervoltage and other protections (some flip-flops and comparators); and finally -- optionally, a micro (like an Arduino, yes) to control the high level things (like current limit or power level, but not the actual switching).At 200W, you don't have much to loose if you run it from an MCU anyway, and the code locks up and it burns up. Or if you just use a dumb power oscillator -- it's fine as long as it's working, but as soon as it stops... pssht BANG. Either can be made useful enough to work, if not really reliable in the grand scheme of things (no way I'd do that for 1kW or 10kW or more).Tim

author: JimStephens
author_rank: Newbie
timestamp: March 10, 2015, 06:16:01 pm
content: Hi all,Thank you for your comments, all have been taken on board. It is a uni project (its coil - cooker)The reason the IGBTs are so big is because it was supposed to be a high power induction heater. I will be testing it with 50 VDC and an Arduino. It probably will never see high power.The 4N25 - I was concerned about the 15VDC driver supply back feeding into the Arduino. The 4N25 was handy to get but I do agree with it been slow. Once I get it powered up I will see what its like.RE gate resistors, caps, oscillators - I will look into making these changes.Thanks again all

author: Siwastaja
author_rank: Super Contributor
timestamp: March 10, 2015, 06:56:12 pm
content: Don't use IGBTs with a 50V supply. It's a huge waste of efficiency. Of course it works, but why use wrong devices that are more expensive, require higher gate drive voltage, and need a large heatsink due to being 10x less efficient than the right device for the job - MOSFET.At higher voltages, IGBT is a good choice, but 50V is just "too far".But whatever, it will work just fine. And if you plan upping the voltage to rectified 230V - that is, 320VDC - then the 600V IGBT is the right thing to use.