How to get 90% duty cycle from TL494?

Discussion in 'General Electronics Chat' started by daviddeakin, Apr 26, 2012.

  1. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
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    I am toying with the idea of making a PWM-modulated audio phaser. I have determined that for the project I will need a PWM signal that can be voltage controlled between 10% and 90% duty cycle. Frequency somewhere between 30kHz and 50kHz should work.

    I have tried using 555 timers for this, but I haven't been able to get the duty-cycle to go beyond about 20%-80%, which isn't good enough.

    I have no experience with PWM controllers, but the TL494 happens to be very cheap. What I want to know is, is it possible to get the full range of duty-cycle from ONE of its outputs? The data sheets suggests the maximum is 45% from each output (making 90% differential), but differential outputs are no use to me...

    Can anyone help?

    Data sheet:
    http://www.farnell.com/datasheets/1447219.pdf
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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  3. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
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    Oops, sorry! Here's the correct data sheet:

    http://www.farnell.com/datasheets/1447219.pdf

    Looking around I think perhaps it is not possible with this sort of IC. Looks like SMPS are almost never expected to run above 50% duty cycle; I will look into other options.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Like you I knew I had read somewhere about getting the 90% PWM from these chips, so I went back and started reading some of my research. You where right in posting the first link for the SG3525 (or SG1524 as the original was known).

    In this link on page #4 at the top of the right column, it tells how to do it. I knew I wasn't imagining it. :) http://www2.microsemi.com/datasheets/sg1524.pdf

    I would think that the TL494 and the SG chips will all work the same for the PWM output. Let us know if you get it working.
     
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