What Mosfets do I use for my H-Bridge ?? Help

Discussion in 'General Electronics Chat' started by howdoesthatworkguy, Jul 23, 2007.

  1. howdoesthatworkguy

    Thread Starter Active Member

    Jul 23, 2007
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    I am building a decoder for my model railroad. It basically users a Microchip PIC and decodes a single from a power supply/command station. Which in turn allows me to control each train independently. This is all called Digital Command Control or DCC. The problem I have is trying to figure out what MosFets to use in the H-Bridge. Trains have a typical 12V CAN motor. Up to
    2A and should not have any noise from the motor. By what I have read I need to make sure it can switch above 20KHz right ? I have also noticed that I would not need to use drivers if I use Logic Level MosFets correct?. So if I use a typical H-Bridge then the high side is going to be P-Channel and low side will be N-Channel. But this is the hard part, the data specs from companies is where I get lost, I am unsure what type of MosFets to choice from. Also, I want them in a SOT3 package, or something in SMD because of space constraints. I was looking at the ZXMHC3A01T8 from Zetex because it was in a very small package as a basic H-Bridge. Others I had a look at were ZXMN2B14FH because it seems to have a low gate drive requriement. But the ZXMN2B14FH is an N channel, and I can't find its P Channel counterpart. Can anyone point me in the right direction ?
     
  2. nanovate

    Distinguished Member

    May 7, 2007
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    Can you post your schematic?

    That's not entirely true, once we get more information about your requirements I am sure someone here can comment specifically on your application.

    This one would push the limit on max current-- little margin above 2A. The thing is that you want to drive it using logic level voltages so the RDS_on will be higher and thus the power dissipation will also be higher. So you'll run hot at 2A which lowers the life of the device.

    Also you can look at the IRF7317 (or similiar) it has a n-ch and p-ch together in a SO-8 package. If you are only needing 2A then this might be an option. But you would need 2 of them.

    ST has a motor driver chip also I think.

    You do not have to get "matched sets";). Look for a P-CH that has the best specs you can find-- they will not beat an N-CH though. Which is why there are several drivers out there that are designed to use 4x N-CH-- Intersil HIP4081A.


    John
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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  4. nanovate

    Distinguished Member

    May 7, 2007
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  5. howdoesthatworkguy

    Thread Starter Active Member

    Jul 23, 2007
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    OK, I have made a serious mistake already. I am sorry if I put everyone wrong, I only need to get 1Amp out of the ZXMHC3A01T8. Does this change anything. It seems you people have such a wealth of knowledge about this. My main reason for this package or others that are small is space.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You're admitting you're human? :eek: ;)
     
  7. cumesoftware

    Senior Member

    Apr 27, 2007
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    Not all people. Take me, for instance...:D

    Don't let our knowledge intimidate you. We are here to help and asking harms nobody. Like Socrates would say: "One thing only I know, and that is that I know nothing."
     
  8. nanovate

    Distinguished Member

    May 7, 2007
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    It is not a serious mistake! :) It certainly is better than saying "Oh wait I need 20A". We are here to help (and learn also).

    1A puts the ZXMHC3A01T8 back into the running :) I looked at the max RDSon at 4.5V and the graphs of RDSon vs temp (for VGS = 10V) and it looks like you should be OK using it for 1A continuous. Now if you are duty cycling it less than 100% then you can have higher peak currents.

    Once you have a schematic please post it.

    John
     
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