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  1. #1
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    Induction Cooktop Circuit Design

    Hi, i need to design induction cooktop circuit having 4kW output power. I have 1kW and lower power levels SMPS background but i dont have any experience in resonant converter topologies. As i have read from app notes, it is very similar to resonant converters except transformer. In formulas, i see transformer turns ratio and output voltage but in this design, i dont know what the output voltage is. I would like to ask whether i can apply the resonant converter formulas to induction cooktop circuit design ? I am struggling applying formulas especially turns ratio and output voltage calculations.
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  2. #2
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    Re: Induction Cooktop Circuit Design

    Your "core" is the pan and your secondary is the pan
    and the secondary "burden resistor" is the pan as
    well. As this is highly end-user-variable I'd think that
    attention should be paid to resonance tuning for
    some coupling behavior (as bounded by wallplug,
    performance and regulatory realities).

    You might look at industrial / metalworking
    induction heaters for inverter designs, there are
    many, RF LDMOS or GaN FETs are likely for the
    power devices, I don't recall much thought given
    to real time tuning in these applications but you
    are looking also for fine heat control where dudes
    melting beer cans for fun, just go full out.

    You could always look for service schematics
    for high end appliances. Although these days it's
    probably "module level replacement by qualified
    personnel".


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  3. #3
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    Re: Induction Cooktop Circuit Design

    Quote Originally Posted by dick_freebird View Post
    Your "core" is the pan and your secondary is the pan
    and the secondary "burden resistor" is the pan as
    well. As this is highly end-user-variable I'd think that
    attention should be paid to resonance tuning for
    some coupling behavior (as bounded by wallplug,
    performance and regulatory realities).

    You might look at industrial / metalworking
    induction heaters for inverter designs, there are
    many, RF LDMOS or GaN FETs are likely for the
    power devices, I don't recall much thought given
    to real time tuning in these applications but you
    are looking also for fine heat control where dudes
    melting beer cans for fun, just go full out.

    You could always look for service schematics
    for high end appliances. Although these days it's
    probably "module level replacement by qualified
    personnel".
    Hi, thank you for your comment. Could you also advice for resonant controller ic ? I have found resonant controller ics such as ncp1399, fan7631 and ucc256303. I also would like to ask whether isolation is needed. We will use plastic enclosure.
    In generosity and helping others, be like a river. In compassion and grace, be like sun. In concealing others’ faults, be like night. In anger and fury, be like dead. In modesty and humility, be like earth. In tolerance, be like a sea. Either exist as you are, or be as you look.



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  4. #4
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    Re: Induction Cooktop Circuit Design

    I'm not sure a "resonant controller" is needed or wanted.
    That naming usually applies to one / some of the resonant
    transformer DC-DC converter topologies. But this in turn
    relates to the complex switch drive needed for snubber,
    source / shunt switches in such topologies.

    In your case what you want is resonant frequency match
    to the funky all-of-a-piece core / secondary / load mess.
    That's not really like the converter application where you
    have a single known fixed inductor-bundle (multiwinding
    xfmr) - you have the problem of a varying LM{LRC} thing
    which you may conceive as a transformer but good luck
    getting secondary-side feedback.

    Wireless power transmission outfits like ChargEdge have
    been putting out a lot of stuff about near field power
    transfer and how to make frequency-tuning for power
    efficiency and scale, work.

    Your cooktop would presumably have a tempered high
    temp glass face that would be the human safety barrier
    at the "business end". There could be "sneak paths"
    that pertain to control knob, case, etc. and you'd
    be wanting a power conversion products type to tell
    you what can and can't be fielded, when it comes
    to that. But for now I expect this is a bare bones
    "get the water to boil, then worry about the logo"
    effort that ought to focus on whether you get the
    top line job, done. Resist scope-creep until someone
    puts a value to it.


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    Re: Induction Cooktop Circuit Design

    Do i need isolation ? As i have seen in induction cooker, only the control circuit was isolated, not the power stage. I missunderstood the project. This project is going to use to heat a metal pipe where water will circulate. Is it ok to insulate only between the coil and metal pipe ?
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  6. #6
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    Re: Induction Cooktop Circuit Design

    That ought to do, especially if the pipe is also earthed.
    Probably wants some attention to durability of the
    insulation against various fault scenarios like water
    intrusion, gross overtemperature (like induction-heating
    a dry pipe) and so on. FMEA fun, miss one and smell the
    freshly baked torts.

    Now you sound like an on-demand water heater, which
    maybe you can find construction tear-downs for that
    can show you what's managed to make it to market with
    adequate (or at least compliant) safety qualities.


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  7. #7
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    Re: Induction Cooktop Circuit Design

    There will be temperature feedback from the metal pipe for over-temperature. For the safety, metal pipe i think should be earthed. We have observed in a product having only plastic insulation between the coil and metal pipe. Maybe we can put HF transformer at resonant converter power stage for the safety.
    In generosity and helping others, be like a river. In compassion and grace, be like sun. In concealing others’ faults, be like night. In anger and fury, be like dead. In modesty and humility, be like earth. In tolerance, be like a sea. Either exist as you are, or be as you look.



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