mofet question, VGSS, & datasheet N or P chanel

Discussion in 'General Electronics Chat' started by Hamlet, Dec 12, 2015.

  1. Hamlet

    Thread Starter Member

    Jun 10, 2015
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    I am curious about how to determine if a MOSFET is either an N or a P channel type
    by reading the datasheet. Often, it state this at the top of the datasheet, but
    I have obtained a 20W60C3 device, and I can't figure out whether it is N or P.

    Also, I see many common moSfets that have gate-to-source voltage of 20v.

    Are there MOSfets with a gate-to-source of 40v? What is the highest gate-to-source
    on easy to obtain Mosfet? I'd like to try one and make a simple 30v 24v, 21v, 41v etc
    mosfet voltage regulator by using a zener, but most only go to 20v on the gate/source
    voltage, so I'd fry or puncture the layer by trying anthing higher than 20v in regulation.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Could you post the datasheet you're referring to? I downloaded one and it's horrible.

    If they followed the typical convention regarding drain current, it's N channel. P channel give a negative drain current.

    Max Vgs is an important parameter, but you also care about Vth.

    Sounds like you're confusing gate to source and source to drain. Max source to drain is a more important parameter.
     
  3. Hamlet

    Thread Starter Member

    Jun 10, 2015
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    Yes, that's problaby the same data sheet I found. Garbage. But I noticed the Vgs (GATE TO SOURCE)
    was 30v, where IRF510, IRF540, IRF640 etc. only have a Vgs of 20v Gate-to-Source voltage.
    I can't make a volt regulator higher than 20v with the IRF540, because applying
    a voltage too high would puncture the ox layer. So, either I find
    a Mosfet with higher voltage, or I skip this project.

    [​IMG]

    I don't want twelve volts, I want more! A 24v regulator, a 36v regulator, and so on.

    I don't know much about all the different kinds of mosfets, I thought I was onto something
    when I found the 20W60C3 mosfet device, because the Vgs is 30v, a nice step in the right
    direction.

    I'm not building a specific project, just doing some bread-boarding, and compiling ideas. If this kind of voltage
    regulator can be built to regulate higher voltages than the gate-to-source maximum, that would make it more useful.

    I've built it, and it regulates fine, but only at voltages below 20v (although I haven't pushed it more
    than 16v, because I can only guess what any individual devices' actual Vgs(th) Gate Threshold Voltage.
    Might be... could be 2v, or it might be 4v, and so on. I subtract this from the Gate-to-Source to find my safe upper limit for regulation.

    (edited 3 times for grammar)
     
    Last edited: Dec 13, 2015
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    The MOSFET you mentioned has a maximum S/D voltage of 600V. Should be fine for what you've mentioned.

    IRF540 is a 100V S/D device. It will also work.

    The circuit you have isn't a regulator. To make a power supply, you need to have a feedback circuit to control the output voltage.
     
  5. Hamlet

    Thread Starter Member

    Jun 10, 2015
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    I know what the S/D voltage is.

    I'm referring to the MAXIMUM gate voltage. The zener limits
    the S/D voltage by holding the gate steady, or something.

    An yes, it isn't the best of regulation, but it could be useful.
    Maybe we can call it the almost-voltage-regulator.

    Are there any mosfets that have a maximum gate voltage of say,
    50v?
     
  6. dl324

    Distinguished Member

    Mar 30, 2015
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    You don't need a a higher Vgs to make a higher voltage regulator. Say Vgs max was 20V. That just controls the maximum voltage you can put on the gate, relative to the source.

    Your circuit isn't functional. To turn the MOSFET on, you need to apply a Vgs greater than Vth. In your circuit, the source has no connection to ground unless a load is connected.
     
    cmartinez likes this.
  7. ScottWang

    Moderator

    Aug 23, 2012
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    If the circuit like that, you can't get a Vs as 12V output, it will output 48V and blow up the capacitor, because the rating voltage of capacitor is too low.
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    You could refer to this circuit.
    [​IMG]
    Circuit source.

    Or you can using LM317HV + IRF540N and plus the circuit as above, R2 used for limited the output current.
     
  9. dl324

    Distinguished Member

    Mar 30, 2015
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    In the schematic Scott posted, the maximum gate-source voltage would be 12V; independent of the output voltage. Maximum S/D voltage is more important.

    For BUZ326, Vgs = 20V, Vth = 4V, and Vds = 400V.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    For BUZ326, the Rds = 0.5 Ω is too high for lower voltage and big current, if using this kind of mosfet over 100V is better.

    For IRF540N, last times I tested the similar circuit, but the voltage less than 24V, it seems that the Vgs about 3V, I think if using LM317HV +mosfet is better than just using mosfet.
     
  11. Hamlet

    Thread Starter Member

    Jun 10, 2015
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    Ahhh, this looks interesting. I also like Scott's idea of using an LM317 + Mosfet,
    which is what came to me upon waking this morning. I'm having internet trouble
    due to stormy weather. I'll try breadboarding this both ways, try to figure out
    what is going on, tune up my definitions, and get back when I can.



     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    The bjt was controlled by current and the mosfet was controlled by voltage, if you want to using LM317 to control mosfet, the range of Vgs only 2~10V can be used, so you have to set the output voltage of LM317 to limited at 2~10V, the first thing is to find out which range of 2~10V is the best range to control the Vgs.
     
  13. hp1729

    Well-Known Member

    Nov 23, 2015
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    Since the data sheet (in any language) states Vds as a positive voltage I would say it is N MOSFET.
     
    Hamlet likes this.
  14. Hamlet

    Thread Starter Member

    Jun 10, 2015
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    Okay, I'm new to the whole mosfet thing. I've built some projects using them, but I'm no expert.
    Mosfets conduct thru the Source/Drain terminals. The gate is like the base of a bjt, but instead
    of current controling the gate, we use voltage. There is a tiny voltage range where the gate is
    either on, or off. In between this, there is a small area where we can control the mosfet to a state
    where it is partially on.

    Yes or no?

     
  15. ScottWang

    Moderator

    Aug 23, 2012
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    You catch the point.
    There are two kinds of mosfets, the one is logical level as Vgs = 4.5V or 5V, this type will be very narrow for the linear area as 2V~4.5V or 2V to 5V, and another type is the Vgs =10V and the linear range as 2V~10V, when the Vgs≥10V then the mosfet will get into the full saturation status, that is the logic conception as the switch on, the Rds will be very low as IRF540N that the Rds(on)=40mΩ, when you want to using mosfet to control its Vgs then you should choosing the type Vgs=10V.

    You can try the right part of the circuit that I linked, it just using the mosfet, if you want to try LM317 + mosfet then you you need to choosing the part of the linear area 2~10V.

    IRF540N -- 33A, 100V, 0.040 Ohm, N-Channel, Power MOSFET.
     
  16. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    It's my understanding that mosfets work better a 'switches' and not as good as 'variable resistances' to regulate voltage. When a mosfet is in its saturated region, not fully turned on, it creates heat. Where a BJT is usually quite happy working to regulate the output voltage of itself.
     
  17. ScottWang

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    Aug 23, 2012
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    That's true, so you can't find the examples easily.

    Whatever the bjt or mosfet, when they are working at the linear region, the heat always following.

    Yes, indeed, easy to use, but we have to concern the heat problem.
     
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  18. shortbus

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    May be another of my misunderstandings, but, aren't the saturated and linear regions different things in BJT vs mosfet? Linear region of BJT is same effect as saturated of mosfet and visa-versa/
     
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  19. ScottWang

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    Aug 23, 2012
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    They are similar, but the bjt is more linear than mosfet when they are at their linear region, you can say that the mosfet is not so easy to control, so most people just want to choose the easy thing to do.
     
  20. cmartinez

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    Jan 17, 2007
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    I think that @crutschow knows the answer to that.
     
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