TL3842 PWM frequncy problem

Discussion in 'The Projects Forum' started by mah, Feb 10, 2014.

  1. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    i used the attached circuit taken from TL3842 datasheet http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=tl3842&fileType=pdf where i used Rt =7.5 kΩ , Ct = 2.2 nf and the output frequency displayed on oscilloscope was 166 KHZ however in datasheet figure 3 page 8 the frequency is 1.72 /Rt*Ct that will mean my frequency should be 104KHZ where is the error here ?
    another question , how to reduce the peak value of pulses . at Vcc =15.5 the output pulses peak was 8 v , i want to reduce it to 1 volt to drive dc -dc buck converter .
    thanks
     
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  2. ScottWang

    Moderator

    Aug 23, 2012
    4,850
    767
    I think you should measure the pratical value of R & C.

    About the output voltage down to 1V, the easy way is to using the voltage divider, if you want something better, shows that what is your dc to dc, and any special request?
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,981
    3,221
    Don't know why your frequency is off. Double check your component values and connections.

    You can reduce the voltage with a resistive divider. Why do you need only 1V?

    The TL3842 can be used to do buck conversion directly with the addition of a few parts. Why do you want to drive a separate buck converter? :confused:
     
  4. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    how to use it directly as buck converter ? would attach the circuit ?
     
  5. crutschow

    Expert

    Mar 14, 2008
    12,981
    3,221
    Here's an application note for the TL3842.

    Why were you going to use this to drive another DC-DC converter? What converter was that?
     
  6. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    it's working thanks it was connection problem
     
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