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PTH08T250W measuring the output ripple

Lars Sterzenbach
Prodigy 40 points

Hi,

i have read the "PTH Output ripple Measurement Methods" paper but I have another question:

Is it possible or even better to measure with an active probe directy at the load, if there are roundabout 25cm

cable between the PTH-module and the load?


Thanks

  • 0
    TI__Mastermind 38230 points

    Hi Lars:

     The best method for measuring ouptut ripple is always across  a ceramic capacitor at output bus any location. The standard method to accurately out noise and ripple is to closely couple the scope probe directly across a ceramic capacitor.

    The standard high frequency FET switching noise is an air e-field stray field always present on all switching power supplies power Inductor... This field has no power associated with it, unlike the sinusoidal lower frequency ripple. The high frequency switching pulses are no present on the conductive output bus plane.  

     The scope probe sensitivity when set to 10 -20mV /div with long 2.5 to 3" ground lead is antenna always picks all distributed fields. By simply moving the long ground scope probe wire position closer and farther away from the inductor can change its pickup field.

    The scope must be set to 20MHz bandwidth and the scope probe must be closely coupled as described in the last attachment.

    Tom