H Bridge Troubleshooting

Discussion in 'The Projects Forum' started by Dinel, Mar 2, 2016.

  1. Dinel

    Thread Starter New Member

    Mar 2, 2016
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    I checked all my data sheets and confirmed that all components were placed properly, which they are, yet my circuit still isn't working. I am supplying 5V from a 9V battery that is going through a regulator. The motor works if placed directly after the regulator, so my problem must be with the bridge. The PNP and NPN are in proper position, so it can't be them either. Any suggestions would be appreciated.
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    Do you have a schematic of what you are trying to build?

    Also, what is driving the bridge? You have resistors to the transistors that do not seem to be connected to anything. How are you turning the transistors on and off?
     
  3. Dinel

    Thread Starter New Member

    Mar 2, 2016
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    It is just a regular H Bridge, and I removed the other connections so that the rest of the circuit could be visible, I'm just trying to get it to work right now so I'm manually connecting the NPN bases to 5V and the PNP bases to ground
     
  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    I was hoping the schematic might answer some questions as what parts are being used as transistors, resistors, and possibly motor. How much current is required by the motor?
     
  5. ISB123

    Well-Known Member

    May 21, 2014
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    Do you have a multimeter?For how much voltage is motor rated?
     
  6. Dinel

    Thread Starter New Member

    Mar 2, 2016
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    It's a 5V motor, and I don't have my multimeter with me at the moment so I'm just trying to see if everything else is right for now
     
  7. ISB123

    Well-Known Member

    May 21, 2014
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    Your motor maybe doesnt work because it's actually working at 3.6V since the voltage drop of PN junction.Try the circuit without the regulator.
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    If you want to learn the EE then you have to learn the right way, you need to draw the circuit as every EE players.

    Bjt H-Bridge_Dinel.jpg
     
    Marcus2012 likes this.
  9. Marcus2012

    Member

    Feb 22, 2015
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    If the low side BJTs are NPNs and 2N3904s then they are the wrong way around. pin configuration is the same as the 3906 (1-E,2-B,3-C). But do you also know the current for the motor as the collector current for these is only 200mA.
     
    Last edited: Mar 2, 2016
  10. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    If you saturate the transistors you should be able to get around 4.5 volts across the motor. This is very dependent on the motor being used and the transistors as well.

    Also, just as a side note. The pinouts of transistor are not all the same. Check the datasheet for the transistor pinout for every new transistor you use.
     
  11. Marcus2012

    Member

    Feb 22, 2015
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    Just as a main note the pinout for the 3904 and 3906 are the same (by ST anyway) as you say always good to check but every pair I've encountered are the same.
    Untitled.png
     
  12. Marcus2012

    Member

    Feb 22, 2015
    349
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    Actually I recall a PN2907 or something that was a complementary NPN TO-92 that had opposite pinout so I stand corrected. This is why a schematic would be useful please :)
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,058
    3,820
    A BC337 and BC327 have reverse pinout from 2N3904/3906. And these BC parts have much more appropriate current carrying capabilities than the 3904/6 parts.
     
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