555 pwm

Discussion in 'The Projects Forum' started by cowboy303, Jan 30, 2012.

  1. cowboy303

    Thread Starter New Member

    Jan 30, 2012
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    This is my first post so hear it goes.

    I was trying to design a PWM using a 555 timer chip with a separate frequency adjust using a pot.
    any body know the best way to do this.

    And what is the difference between the LM555N LM555CN NE555N and every other one. And witch one would I want.

    Thank you all for your time
    And please tell me if I'm doing anything wrong thank you again
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,135
    3,054
    Welcome to the forums. It would help if you could provide more details about your application. That's how you might choose between different specs for the 555 timer. Things like power supply type, voltage and current specs, target operating frequency of the PWM, anticipated load on the output, are all factors.

    The devil is in the details. ;)
     
  3. cowboy303

    Thread Starter New Member

    Jan 30, 2012
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    0
    Power supply 12volt battery now 12volt wal-wart later
    not sure what you mean by current
    load just a 2n3055 transistor
    frequency 500 to a few thousand (as high as posible)
    thank you
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,135
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    The base current of the 2n3055 may be 10% of the collector current, which can be quite high. In other words you might be putting a bigger load onto the 555 than it can handle. What is the 2n3055 controlling?

    Your "low" frequencies shouldn't be a problem.

    A wall wart is unregulated, which means the voltage will vary with the load. With little load, it might be over 16v. Under increasing load, the voltage will come down and the ripple will increase. A big ripple may cause timing problems. Is your main load - the one being controlled by the 2n3055 - also powered by the wall wart?
     
  5. Brownout

    Well-Known Member

    Jan 10, 2012
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    Hi Cowboy. There is a very good method I've used that takes the output pin through a couple doides which are in turn connected to opposite ends of a center-tapped variable resistor, which then feed the timing network. I have a schematic at home, if nobody else posts it by the time I get there, I'll put it up.
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,173
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    Not all wall warts are unregulated, find one rated around 70 V AC to 240 V AC input & fairly light, will be switch mode & regulated.
     
  7. cowboy303

    Thread Starter New Member

    Jan 30, 2012
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    The 2n3055 would be controlling 500ma MAX

    The wal wart I would use with no load is 14volts (Tested) and is rated for 1.2 amps and if I put a 2200uf cap across the leads would that take out the ripple
     
  8. wayneh

    Expert

    Sep 9, 2010
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    That should all be fine. Just search this site for 555-based PWM circuits. Take a look here, for instance.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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  10. wayneh

    Expert

    Sep 9, 2010
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    Thanks, Bill, that's the link I was thinking of but couldn't quite recall. Should get the OP well on his way.
     
  11. cowboy303

    Thread Starter New Member

    Jan 30, 2012
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  12. Brownout

    Well-Known Member

    Jan 10, 2012
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    Honestly, I wouldn't buy from e-bay, no matter how cheap they may be. I'd buy from Digi-key. That way you know you're getting good parts.
     
  13. wayneh

    Expert

    Sep 9, 2010
    12,135
    3,054
    FWIW, I've had good luck on e-bay so far. But most here will say I'm just that - lucky.

    Anyway, look at datasheets for the meaning of the suffix letters. If one manufacturer doesn't address it, try another.
     
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