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Wide Range off-line switcher

Discussion in 'Electronic Design' started by Pierre de Vos, May 7, 2004.

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  1. Hi,

    I need an off-line switcher with a very wide input range. Typically
    50Vac - 555Vac. I have seen a motorola appnote describing an offline
    switcher that approaches this range, but from what I can remember that
    one had a 6:1 input ratio. The one I need is 10:1.

    Anyone have any ideas?

  2. legg

    legg Guest

    At what power level?

  3. Terry Given

    Terry Given Guest

    The motorola app note was a low power flyback converter (< 50W IIRR). Marty
    Brown's cute trick was to organise the frequency to vary with input
    voltage - IIRC to get constant volt-seconds, ie Fsmps = k*Vin

    One way to get a wide input range is to run your smps at low frequency (say
    30kHz) BUT use a fast switch/controller, so you can have very narrow duty
    cycles - the duty cycle limitation is what causes "squegging," as its sets a
    lower bound on the energy quanta delivered to the load; for lighter loads
    the voltage rises, forcing the error amp to set D=0 until Vout sags....A
    known minimum load can be helpful in this regard.

    Keith Billings' book has a suggestion whereby he transitions to fixed on
    time, variable off time at very light loads.

    Like R.Legg says, how many watts?!?
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