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PWM with SG3525

Discussion in 'Electronic Basics' started by parkc23, Aug 13, 2004.

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  1. parkc23

    parkc23 Guest

    Hi, could anyone help me with SG3525? I have a PWM circuit with
    SG3525 and need to modify the circuit so that I can get ~0.2 Hz cycle
    period. This is very slow compared to most of the circuits that I can
    get.
    Probably, I can change the frequency by changing the capacitor or
    resistor at Rt and Ct (pin 5 and 6), but I don't know the equation to
    calculate those.
    Please help me!!!
     
  2. CFoley1064

    CFoley1064 Guest

    Subject: PWM with SG3525
    How do. For questions like this, nothing beats the data sheet:

    http://www.st.com/stonline/books/pdf/docs/4286.pdf

    It says the approximate frequency is:

    1 f = 1/(CT (0.7 RT + 3 RD))

    However, the datasheet also says the minimum practical frequency for the SG3525
    is about 100 Hz. If you're looking for 0.2 Hz, you'll have to look for another
    PWM IC, roll your own PWM with an op amp or comparator, or just use a PIC. The
    last solution is probably the preferred one if you need a PWM which has a 5
    second cycle time.

    Good luck
    Chris
     
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