---
+ Post New Thread
Results 1 to 2 of 2
  1. #1
    Member level 5
    Points: 1,677, Level: 9

    Join Date
    Jun 2006
    Posts
    84
    Helped
    0 / 0
    Points
    1,677
    Level
    9

    voltage drop formula

    what factors effect the voltage drop on PWM dc-dc converter?

    •   Alt15th September 2009, 13:35

      advertising

        
       

  2. #2
    Super Moderator
    Points: 21,986, Level: 36

    Join Date
    Mar 2008
    Location
    USA
    Posts
    3,310
    Helped
    951 / 951
    Points
    21,986
    Level
    36

    why current drop in pwm

    The voltage drop input-output? That's the step-down
    ratio which becomes roughly the PWM duty cycle,
    VOUT/VIN. The drop is (duh) VIN-VOUT.

    The voltage droop, or load regulation, is pretty much
    just the error amplifier (and powertrain) composite
    gain as a chopped transconductor. If you are current
    mode controlled then you have a volts-in, current-out
    relation somewhere in there (say, 1A/V) and a volts/volts
    error amp gain (say, 60dB=10,000). So at the error amp
    input you would see for a 1A load step, a 1/10,000 (or 0.1
    mV) input deflection. Now scale that up by the feedback
    network ratio (say, 5:1 for a 28V to 5V buck) and you get
    a 0.5mV output deflection. All happy, right?

    Well, probably not. A major, major term in load regulation
    is the current induced offsets in the ground and the feedback
    lines, which develop current-dependent error voltages. If
    the load current return and the PWM ground are offset,
    this may go right into the error amp (prime reference is
    chip ground, != package, !=board ground). You would like
    a Kelvin ground and load sense, but this is not always a
    practical thing.



+ Post New Thread
Please login