Hex Buffer Decreases Voltage?

Discussion in 'General Electronics Chat' started by will3330, Feb 24, 2011.

  1. will3330

    Thread Starter New Member

    Feb 24, 2011
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    We are using a 4050 Hex buffer to amplify the current from a voltage signal of 5V to run a unipolar stepper motor. The problem is that when we send the signal through the buffer, the voltage on the output decreases to 2V which isn't enough to power the motor. We tried replacing buffer with another one but that did the same thing. Is there any reason as to why this is happening?

    Thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    There may be a difference between the current the 4050 can handle and the current the motor needs for operation. Try looking at the data sheets. That 4050 is a buffer for going from CMOS to TTL more than a power booster.
     
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    A 4050 buffer is not for driving anything other than another logic device.

    Outputs can sink and source only about 1mA if you wish to maintain the correct output voltage to drive CMOS inputs. If there is no need to drive any inputs the maximum current is about 5mA with a 6V supply, or 10mA with a 9V supply (just enough to light an LED). To switch larger currents you can connect a transistor.
    From; http://www.kpsec.freeuk.com/components/cmos.htm
     
  4. will3330

    Thread Starter New Member

    Feb 24, 2011
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    K thanks. However, we are now amplifying the signal to a 74ls194 shift register and then buffer that to the motor. But, the problem is still there. :(
     
  5. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Post your schematic.
     
  6. will3330

    Thread Starter New Member

    Feb 24, 2011
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  7. Papabravo

    Expert

    Feb 24, 2006
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    A logic device is good for maybe 6 to 24 mA. I'm guessing your motor needs more than that. The more current it tries to pull the lower the output high voltage. You are seriously stressing those parts. Post the specs for the motor as well.
     
  8. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Use a SN754410 quad half bridge or ULN2803, the 4050 isn't powerful enough.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Wait a minute - your 4050 outputs appear to be going to an L298 H-bridge. Is that correct?

    Tell us more about the motor you're using - is it bipolar or unipolar? I see "unipolar" written over by the PIC16F877, but an L298 is a dual H-bridge - why use that when you'd be better off driving it in unipolar rather than bipolar?
    What current and voltage rating?
    And what voltage are you driving it with on the L298 connections?

    You won't be able to drive a motor using an L298 with a motor supply of 5v. The L298 will drop about 4v across itself even with just 1A current.
     
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