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Re: [beam] Tilden H-bridge

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  • Eljin
    Thanks Wilf. You were right on the money with my first bridge. The second one is putting out the voltage, but obviously not the current. I think though that my
    Message 1 of 4 , Apr 30, 2005
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      Thanks Wilf. You were right on the money with my first bridge. The second one is putting out the voltage, but obviously not the current. I think though that my problem is having a mismatched transistor in there.

      Worse, after reading what you said about the inputs, I'm figuring out that this particular bridge is not what I need. :-(
      Besides, when I didn't get an answer for a couple of days and couldn't figure it out on my own, I started researching other units. Units designed for what I'm trying to do. I also found out that I could get the parts as samples, which is a huge boon to me as I have almost no budget to work with.

      I'm looking forward to getting this one up and running soon. Then the fun can really begin... :-)
      This is to be a research vehicle that I can expand upon. I'm going to eventually morph it into a biped after getting most of the bugs out of the software.

      Thanks again. You have been most helpful, not only this time, but before. I've been to your web site several times. It's awesome! I wish more people would take the time to do such an awesome job of explaining things as you have.
      I think you ought to add the troubleshooting tips you gave me to your site. They took me directly to the problem.

      Later,
      Eljin

      Wilf Rigter wrote:
      I assume that means that the motor turns when one input is active but does not turn when the other input is active.
       
      NOTE:    Be sure to only take one input to the active state never both at the same time.
       
       
      The fact that both suffer from the same problem  probably means one of the transistors is wired backwards. 
       
      A  transistor with the collector and emitter swapped will still work if the supply voltage is less than about 6V but the current gain is no more than 1 or 2.  
       
      This means that without  a current load, the voltage measurements may look normal but it just won't be able to supply much current.  
       
      You can visually inspect it or do some tests on the h-bridges.
       
      Best way to check it out is by holding  the one input of the h-bridge active that does not result in motor motion.
       
      Now the motor is used to test the current capability of the outputs as follows:  
       
      1) Connect motor between GND and output A - does it turn?
           a) YES - active NPN output transistor is reversed or bad.   
           b) NO - go to 2
      2) Connect motor between +V and output A - does it turn?
           a) YES - active PNP output transistor is reversed or bad.
           b) NO - active input driver transistor is reversed or bad.
       
      wilf
       
      ----- Original Message -----
      From: Eljin
      Sent: Thursday, April 28, 2005 8:48 AM
      Subject: [beam] Tilden H-bridge

      I'm trying to finish my last two h-bridge circuits, but am having a problem.
      These two will only spin the motors in one direction. I've checked out
      my transistors and they still check good.

      I followed my wiring diagram to the letter.

      Could some one give me some clues as to why they are not working?

      Eljin


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