thermally protected P-MOSFET with a 10 to 20A capability?

Discussion in 'The Projects Forum' started by russian, Jan 1, 2015.

  1. russian

    Thread Starter Member

    Sep 1, 2012
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    thermally protected P-MOSFET with a 10 to 20A capability - does it exist? Am i failing to find one because I am not supposed to need one, and use low-side control instead?
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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    It exists if you build thermal protection into your circuit, but if you have adequate heatsinking, you should not need extra protection.

    Why do you want it?
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    What do you mean by thermally protected? All modern FETs are, to some extent.

    DigiKey lists hundreds of them. Use their search tool to focus in on what you want...
     
  4. russian

    Thread Starter Member

    Sep 1, 2012
    55
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    Maybe all, but FQB12P20TM has recently un-soldered itself and has fallen off the board due to my mistake with selecting the right duty cycle parameter.

    I am looking for build-in thermal shutdown in case something does wrong and I apply the wrong duty cycle.

    digikey does not allow me to filter for that feature and the ones I am looking at do not have it.

    "The location of the sensing element on the chip in the power stage area ensures fast, accurate detection of the junction temperature. Over temperature cutout occurs in the range 150 to 190 °C, a typical value being 170 °C." - that's from the low side driver datasheet. I am looking for more or less the same deal but in a high-side switch.
     
  5. LDC3

    Active Member

    Apr 27, 2013
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    Most high current power supplies use multiple FETs to supply current above 5A so the heat is distributed. I'm guessing that your circuit board doesn't have room for more than 1 FET.
     
  6. DickCappels

    Moderator

    Aug 21, 2008
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    That's funny, back in the early 1980's when MOSFETs with logic level gate drive capability first appeared, I switched a motor drive amplifier using Darlington transistors to MOSFETs. It ran much more smoothly, but what impressed me was when there was a circuit fault, the MOSFET would unsolder itself and fall off the PCB but be completely unharmed, where before the Darlingtons would be "permanently dead".

    ]If this is a problem for you, I suggest that you spend some time to determine why your MOSFETs are over-heating and if at all possible arrange things so that this cannot occur - better drive waveform, more appropriate operating voltage and gate drive, better load handling, the right MOSFET, and enough heatsinking. You really must get this all correct before you have a good working circuit. Protection circuitry is a back up for unexpected problems; it is not the solution to a poorly designed circuit.

    After designing a circuit that works well, you can protect your circuit from unexpected problems by adding a current limiting circuit.

    http://ts4.mm.bing.net/th?id=HN.607992160631064372&w=223&h=140&c=7&rs=1&pid=1.7
     
  7. russian

    Thread Starter Member

    Sep 1, 2012
    55
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    Oh I know when the issue occurs - the issue occurs when I apply too much of duty cycle which controlling this with micro controller. While sure, I am hoping to have the code so that duty cycle is limited to 25% which is totally good enough for me. What I am looking is a fall-back plan if for example my firmware hangs up due to a software issue of some sort. The current limiting circuit looks like a number of components thus a lot of real estate on the PCB. A MOSFET which would simply shut down and then revive once things cool down would be so much simpler, if only it existed in the P-mosfet universe :)
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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    You can use a NFET with bootstrap or charge pump. I don't know why there are not PFETs. Current limit might be easier.
     
  9. DickCappels

    Moderator

    Aug 21, 2008
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    A thermally-protected MOSFET was the original question. I don't think that devices known by this name exist. Maybe somebody will prove that statement false.
     
  10. russian

    Thread Starter Member

    Sep 1, 2012
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    1
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