TRIAC vs. IGBT

Discussion in 'General Electronics Chat' started by Davidpostlethwaite, Mar 2, 2008.

  1. Davidpostlethwaite

    Thread Starter Member

    Mar 2, 2008
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    I'm looking to turn a heater (2kW, 1-ph, 230Vac).
    I have managed to do this using a triac and PIC so I can dim the heater (vary it from 0kW to 2kW) using a small POT on the PIC input.
    A triac, once triggered, remains on until the next crossover point before requiring its next gate trigger. This means the heater can only be switched on in the latter parts of each mains half cycle. I need the heater to switch on from a zero crossover point and remain on for a time (set by my POT) before turning off half way through that cycle.
    This means I'd be taking power from the start of each half of the mains sinewave and not at the end of each sinewave (like I've been doing using a triac).
    Does anyone know anything about IGBT's? I've been told they might hold the answer.
    Thanks in advance.
    David Pos
     
  2. rwmoekoe

    Active Member

    Mar 1, 2007
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    do you have to use the pic?
    if not, a simple light dimmer circuit with slight changes or addition at the driver triac to accomodate the 10 amp current will do.

    by the way, a common practice is to turn the triac on somewhere after the zerocross point up until the next zerocross (where the triac will disengage itself), not the other way around.
     
  3. Davidpostlethwaite

    Thread Starter Member

    Mar 2, 2008
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    Thanks. I am currently using a triac which switches ON sometime after the first zero crossover before turning its self OFF at the next zero crossover point. This works really well but I'm planning to use this circuit to control lighting and apparently the bulbs last longer if they are switched at the start of the cycle then turned OFF before the next zero crossover point? something about cold switching and bulb filaments vibrating/breaking?
    I need a device that will switch on at the zero crossover point and then force OFF before the next zero crossover point.
    I am new to this world of IGBT's/ SCR's/Triacs/Diacs/MOSFETs/JFETs etc...
    I'm sure there is the perfect solution out there somewhere! Then, once I've found the device, I'll need to control it some how?
    If anyone can shed some light on the matter I'd be really thankful.
     
  4. rwmoekoe

    Active Member

    Mar 1, 2007
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    i see, that way you need to use igbt.

    you're right about cold switching.
    if you still want to use triac, maybe it can be simulated by switching it on gradually from 0% to the intended level over say 10 or more cycles.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    There are zero crossing detectors that will gate the triac on at that point, and there are gate turn-off devices (GTO triacs) that can be forced out of conduction by a negative pulse on the gate.

    SCR's and triac's are AC devices, the IGBT's and FET's are DC only. For incandescent lamp control using DC devices, you would need to rectify the line voltage and use PWM for the dimming. That is a fairly expensive way to go.

    The zero crossing switching is not all that necessary - once the filament is hot, it will not cool significantly before the next shot of current. Another thing to keep in mind is that it may be that incandescents will be taken off the market in the next several years in favor of fluorescents.
     
  6. rwmoekoe

    Active Member

    Mar 1, 2007
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    those are a good informations beenthere, thanks...
     
  7. Davidpostlethwaite

    Thread Starter Member

    Mar 2, 2008
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    Thanks, I'll look out for GTO Triacs! I didn't know they existed.
    Thanks rwmoekoe and beenthere. This is porbably quite a complex project so i appreciate being able to ask the questions and actually get answers.
     
  8. Davidpostlethwaite

    Thread Starter Member

    Mar 2, 2008
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    I've been looking for GTO triacs in the 40A range and can't find any?! I've checked RS, Farnell, and google searched for 'GTO', 'SCR' Thyristor and can't find a single part number for a device in the 30 - 40A range. they're all 3000000000000A or higher!!!!!!!
    If anyone knows of a GTO Diac or Triac I could use please let me know because I'm all out of ideas. Thank you.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    They are mentioned all over, but I can't get to any information like part numbers. IXYS ha them in the product line, but I can't get to any devices from the web page. None of my catalogs that list IXYS products have GTO triacs listed.

    They may be strictly for humungo power management.
     
  10. Davidpostlethwaite

    Thread Starter Member

    Mar 2, 2008
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    Yea same here, thanks for looking. I just had a thought, will a solid state relay do my job?
    I want to turn a heater on at the START of a half cycle and off somewhere in the middle of that half cycle. Obviously I'd also like the heater to come on at the START of the negative half cycle and off again after the same time period as the +ve half cycle.
    I suppose a solid state relay is similar to an GTO triac?

    beenthere, you seem to be the only one able to answer my questions. Thank you.
     
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
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    No, a relay is definitely too slow for switching at 50/60Hz, and the arcing would kill the contacts very soon.
     
  12. Davidpostlethwaite

    Thread Starter Member

    Mar 2, 2008
    12
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    No sorry, I meant an 'SSR' (solid state switch). I've been looking at them and they require 2mA at 3 to 5Volts to switch ON and anything under 1Volt to turn OFF. The contact side can react in 20uS.
    There are two types, 'zero switching' (which switches at the nearest zero crossing points) and 'random turn ON'.
    CRYDOM make the HD4890-10. I've ordered one so it should be here tomorrow. I'll try and control the ON and OFF state in the middle of a half cycle. It's amazing what's about now.
    cheers.
     
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