I can't find the values of the currents

Discussion in 'General Electronics Chat' started by Oussama Zaidi, Jun 29, 2016.

  1. Oussama Zaidi

    Thread Starter Member

    Mar 1, 2016
    53
    0
    Hi
    The picture below is on page 7 of the datasheet of TL497, it is a switching regulator that I use as an inverting regulator (it has an inverting mode) to generate -24V from 12V in input, in the first designing equation on this page I have 2 unknowns "I(pk)" and "Io max" I don't know how can I find their values ?? In the datasheet it is wrote that I(pk) maximum value is 500mA so if I(pk) in the equation means 500mA why they didn't write 500mA simply unless of I(pk) also I(pk) max value is 500mA it can be lower than that and if 500mA means the "Io max" then I(pk) value will be 3A for VI=12V and |Vo|=24V which is impossible because I(pk) max =500mA. I hope I explained well.
    datasheet:http://www.mouser.com/ds/2/405/tl497a-405896.pdf
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  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,386
    496
    It might be other way around. You know what your load will be, you know how much voltage it will need, you know how much current it will need. It would make sense to plug those two values in and find the Ipeak. Then compare the calculated Ipeak to the 500 mA specification. Note that they show less than 500 mA, not less or equal to. So you definitely want to be below the 500 mA requirement.

    So the question is. Do you know your load?
     
    Last edited: Jun 29, 2016
  3. Veracohr

    Well-Known Member

    Jan 3, 2011
    550
    75
    Io(max) is the maximum current the load will draw, which isn't the same as the peak switching current I(pk). Io(max) shouldn't be unknown, you have to calculate it from your load requirements. 500mA is the maximum value the component can handle for I(pk). So with a 12V input and 24V output the part can provide 500/(2*[1+24/12]) = 83mA to the load.

    If you need more than 83mA use the circuit with PNP pass transistor.
     
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