Is it a Thyristor or MOSFET?

Discussion in 'General Electronics Chat' started by hazim, Aug 18, 2011.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Hi all.

    This maybe a hard job but I'm trying to do it. I have a hear iron to repair. The temperature can be adjusted by a small potentiometer. A TO-220 component (without the metal back) is damaged, it is broken into two parts, the front part that contains the part number "disappeared", maybe it had fallen somewhere but I couldn't find it. So this is the unknown part that I want to know.

    I made a picture to clarify how it is connected in the circuit, without reverse engineering all of the circuit.. and took a picture for the circuit board.

    I had a small 220V-110V wall adapter that is in the size of a 220V to 9VDC 500mA wall adapter, or a 220V-110V 50W wall adapter. But this adapter that I'm taking about was something like 2500W or even more!. It was used with an electric coffee maker. I'd opened the adapter and found that there is a very small circuit with a thyristor mounted to a big block of aluminum that was almost taking the size of the adapter. I know Thyristor transformers are used with resistive loads only, and I think they use phase shifting to "transform" voltage.. I'm taking about this because the hair iron is also a high wattage resistive load. One final thing to say is that the Thyristor/MOSFET/?? in the hair iron is not mounted to a heatsink and it even don't have the metal back that could be mounted through.

    Any ideas?

    Regards,
    Hazim

    [​IMG]

    [​IMG]
     
  2. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Offcourse after identifying whether it is a thyristor or MOSFET or whatever we will try to know it's main parameters.
    The hair iron isn't a high wattage device as I said, it's written on it: 45W (max 300W).
     
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    It doesn't look like a MOSFET. You will have to draw the whole circuit in order to understand what it could have been. Especially the part from input AC to/through the thyristor/triac and then to the load.
    Is this a two or multilayer board? Except for the 200k/LED is there nothing else connected to the left pin?...
     
  4. debe

    Well-Known Member

    Sep 21, 2010
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    In those types of aplications its most likely a triac as that is what is generaly used for switching AC. That one was a surface mount type. The big question is why did it blow? is there a fault in the heater element?
     
  5. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    It is a two layer board. Actually it's hard a little to reverse engineer the whole circuit, and also there is an 8-pin smd IC with the part number swabbed (cleared). I think the info that I gave can help us predict what is this part and even general specifications about it.
    So it's most likely a triac?
    debe, the heater elements are ok, maybe it blown because of voltage higher than 220V... yes that happens here!
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    There has to be something else connected to the left and right pin of the component. Provide at least the power part connections from mains to component and to the load. also provide load resistance.
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Since all the other parts are marked on the silk screen, I bet if you bend the broken part up from the board it will either have a text or symbol telling what it is. Probably not an actual part number ,but, something like - mos1 or tri1. The part does not look in the photo to be surface mount, but rather through hole.
     
  8. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    The right pin is connected only to the diode as in the diagram. the left pin is connected to one of the two resistive loads. See the new picture in this post.
    Right, I found under the part a text "UT1", what that means? it's not "Tri1" or "M1" or "Q1" or even "U1". It isn't a surface mount part... but through hole....

    I found that there is a 20V zener along with some other components that powers the SMD IC. I think this IC is a timer/pwm IC and the potentiometer varies that duty cycle of the output that is connected to the right pin of the Thyristor/MOSFET. So this could be a a high voltage MOSFET and changing the temperature happens by changing the duty cycle.. I know that the order of most (maybe all) MOSFET pins is G,D,S from left to right, but the output of the IC is connected to the right pin... but, a big but! one of the resistive loads is connected directly and only to one pin of the smd IC!!! The first thing I said in this thread is that is a hard job :)

    [​IMG]
     
  9. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    It's definitely not a MOSFET. It is most likely a triac. The right pin is the gate, the other two pins the anodes/cathodes. Now it's getting easier.

    It would be necessary that you provide the resistance from L2 to COM (the load) to rate the triac. Try to find out what package it was, measuring it's dimensions (from what is left)

    Then, if the connection from L1 is correct in your drawing it's not clear what this one is doing since it has nothing to do with the power part.. some kind of thermal protection maybe to shutdown the IC ?
     
  10. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Know I found how it's connected(the load). We have 'L2' is for both iron plats, they are connected in parallel and there overall resistance is 590 Ohm. 'L2' isn't a load but as you said it's for thermal protection. Know we have 220V/590 = 0.37A, it's your turn.
     
  11. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    On the circuit board, you can see it in the picture in 1st post, at the left the text written is COM and RT and LOAD :)
     
  12. praondevou

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    Jul 9, 2011
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    You meant L1, right

    See the attached pdf. you didn't mention the package dimensions. It looks like I-Pak or something similar. I did a fast search on digikey.

    For the voltage rating I chose 600V. If you think you can live with 400V it's ok, but you may be safer with 600V, especially if your mains is not very stable.
    Now, you said somewhere it says "max 300W" on a label. How is this with 590R resistance? Is there something else connected?

    However , I chose 4A components, it was the smallest rating available at digikey anyway, for this package/voltage.

    Now you have to see with your local component supplier, what is available in your country. Just make sure, the one you buy has the gate on the right.
     
  13. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Yes I meant L1. I can't know all the dimensions because it's broken into two parts, but the height is 6mm and the width is 10mm (IPAK's height is 7mm and width is 6.6mm).
    Nothing connected else connected. Anyway a 600V 4A or more should work.. Know I have another problem, I can't assembled the unit because of that string at the joint of the two parts of the hair iron.. mechanical problem.. :)
     
  14. walkura

    New Member

    Jan 11, 2007
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    Its a bit of a guess with this much info, but wouldn't it be a triac (or thyristor)
    The gate is on the right side (as with the thyristors and triacs i used over the years, not as with mosfets or IGBT's on the left side)
    Also the gate is connected more or less as we did it with MOC3020.
    This setup for gatedriving is used for triacs or thyristors, because for mosfets (or igbt) the diode would be paralleled with a resistor.
     
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  15. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I found Triac AC05F (600V, 5A, IGT<10mA) with gate on the right. I will cut it's metal back and try it tomorrow :) I need a 20V 1.3A zener also, I don't know if I have one... I'll write down what happens with me.
     
  16. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Good luck. If it doesn't turn on the triac, try to measure the voltage at the IC output, the one that goes to the gate. If you have an oscilloscope at hand of course, not with a multimeter.
     
  17. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I have an oscilloscope. Let see tomorrow what happens... Could the terminals T1 and T2 be in reverse of the original bad one?
    BTW the moderators should delete your picture because it's dangerous on young amateur in this forum, the moderators several times gave me lessons when I talk in a subjects related to mains voltage.
    Regards,
    Hazim
     
    Last edited: Aug 20, 2011
  18. praondevou

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    If it's a triac it doesn't matter how you connect T1 / T2.
     
  19. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Ok. I'm not familiar working with Thyristors. Doesn't it need a heatsink? and does triacs have something like Rds in MOSFETs?
     
  20. praondevou

    AAC Fanatic!

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    The power is obviously so low that the engineers thought they wouldn't need a heatsink. Triacs and thyristors have a forward voltage drop. (like a diode)
     
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