Heres yet another trick I use for all my test schematics to measure input current, efficiency, and total internal power dissappation. Since I use this approach universally I automatically add the necessary components and steps as a template for all my schematics, thereby greatly reducing the task.?Time can also be saved by using a standard nomenclature for the parts such as Rin1 for the input test resister, etc. Once you have done this to a schematic the resulting label
formula's can be copied and pasted from schematic to schematic so only slight modifications will be necessary with new circuits.
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1) Add a network in the input line between the test circuit and DC power source consisting of a 1 microohm (0.0001 ohm) resister in parrallel with a 1000000 uF capacitor. The capacitor is used to suppress excess ripple and improve integration accuracy.
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2) Make one display panel to show input current by
clicking on the resister. Add "*-1" to the panel label for positive current flow if necessary.
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3) Make another display window that will show overall efficiency by clicking on the resister for current and then modifying
the label to the calculation form:
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(v(out1)*I(Rload1))/(v(in)*I(Rin)*-1)
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Note: If there is more than one output voltage/current from the power supply circuit under test then add to the numerator of the formula thus:
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((v(out1)*I(Rload1))+(v(out2)*I(Rload2)).....+(v(outn)*I(Rloadn)))/(v(in)*I(Rin)*-1)
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4) Make a third display window that will show overall internal total power dissapation by first clicking on the resister to set the display to input current and then changing the label to the calculation form:
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(v(in)*I(Rin)*-1)-(v(out1)*I(Rload1))
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Note: again if there is more than one output then the power dissapation of each output must be summed as follows:
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(v(in)*I(Rin)*-1)-((v(out1)*I(Rload1))+(v(out2)*I(Rload2))....+(v(outn)*I(Rloadn)))
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Additional note: It may be neccessary to add a "*-1" multiplier if a negative output voltage is to be added into the calculations. The wrong sign will result in subtracting instead of adding to the overall dissappation. If you are unsure run a window with that output seperated to show the calculated output power to make sure it is positive, adding the "*-1" if neccessary to correct that portion of the formula.
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- The "*-1" added to the input current
label and input power portion of the formulas is to correct for current flow as positive.
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- After the analysis run is complete the integrated values of each panel display measurement?can be displayed by using the mouse cursor to select a range of clock pulses from the display panels. I generally try to select at least 40 to 100?clocks for good integration accuracy. The integrated measurement is then displayed in the usual manner by holding down the
key, positioning the mouse cursor over the panel label of interest, and left mouse button clicking. I often enter the data as text in a tabular format right on the schematic so it will be automatically saved for future reference.
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- A final note. Before making the measurement steps use the "*1" trick added to any of the panel labels?to force vertical expansion. This allows input ripple currents and output ripple voltage peak to peak values
to be measured off the panel traces easily using the mouse cursor "box" feature to display the value at the bottom of the screen in the dynamic data line. Either adding or subtracting the "*1" to/from the label will result in forced vertical?expansion without effecting the calculated values.
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Cordially - RC
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On Monday, December 30, 2013 1:57 PM, "sawreyrw@..."
wrote:
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Jungyeon,
You could just measure the input and output power and compute it yourself.? The help file on steady also tells you how to do it if the steady state criteria is too tight.
Rick
