555 PWM Question.

Discussion in 'The Projects Forum' started by NM2008, Sep 23, 2008.

  1. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Hi,
    With regard to the 555 PWM circuit,
    Could somebody tell me what would a general frequency for controlling motors be.
    Would this depend on the application,i.e voltage, current and range of rpm or is there a general frequency range to stay between, for efficient operation and avoiding overheating.

    Thanks for the help,
    Regards NM
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Everything's a trade-off.

    If you get the PWM frequency above around 25kHz, it'll get out of the audible range (for most humans, anyway.) However, the higher in frequency you run a circuit that is essentially producing a series of square waves, the more carefully it must be designed, and the more current will be used in charging/discharging the gate(s) of the MOSFET(s). Otherwise, the MOSFET(s) will spend more and more time in the transition (linear) region, where they dissipate power as heat.

    So, to keep the design simple and minimize losses due to heat, it's good for hobbyists to run PWM controls at lower frequencies; around 1kHz. The circuit/motor may "sing", but it has a much better chance of surviving.
     
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