7 Replies Latest reply: Oct 10, 2012 10:12 PM by leoglh2001 RSS

Basic knowledge about power test

leoglh2001 Level 7

What is Power? How many kinds are they and how to calculate it accurately?

  • 1. Re: Basic knowledge about power test
    YT2095 Level 8

    Power is the rate at which Energy (the ability to do Work) is used, in electrics/electronics this unit is typcally the Watt, which is taken to be Current multiplied by Voltage.

  • 2. Re: Basic knowledge about power test
    leoglh2001 Level 7

    You reach the conception of Power.

     

    Power, there are transient power, apparent power, active power, re-active power, we can use oscilloscope to calculate the square of Power waveform by using integration.

    Apparent power = UI, unit: VA;

    Active Power =UI*cosθ,unit: Watt;

    Re-active Power =UI*sinθ, unit:Var

    Power Factor= cosθ

     

     

  • 3. Re: Basic knowledge about power test
    leoglh2001 Level 7

    Add some information about Active Power.

     

    It is always calculated as following,

     

    有功功率计算公式.jpg

  • 4. Re: Basic knowledge about power test
    leoglh2001 Level 7

    Using LeCroy oscilloscope, we can test power as shown in below picture,

     

    LeCroy Power test.jpg

    Remarks:

    1 The yellow waveform is voltage waveform;

    2 The blue waveform is current waveform;

    3 The orange waveform is power waveform.

     

    For LeCroy WaveSurfer series oscilloscope, they can test all these power parameters automatically by selecting a PMA2 option.

  • 5. Re: Basic knowledge about power test
    leoglh2001 Level 7

    One of the most difficult in power measurements is in-circuit dynamic saturation voltage across the switching device.  To understand why, we need to look at the waveform itself.

    Before the device turns on, it will have hundreds or even thousands of volts across it.  When saturated, this voltage drops to only a few hundred mV.  An accurate saturation voltage measurement requires a resolution of less than 100 mV.  The measurement system must be able to handle the off state voltage and still resolve to 100 mV.  The requires linearity, overdrive recovery, AC compensation and signal to noise performance of  250 PPM - far beyond what the analog front end of an 8 bit DSO can provide.

    To effectively make this measurement, an external high performance differential amplifier is required.

     

    饱和电压.jpg

  • 6. Re: Basic knowledge about power test
    leoglh2001 Level 7

    We can draw a list of what items should be tested when we test power,

     

    1 Apparent power = UI,

    2 Active Power =UI*cosθ

    3 Re-active Power

    4 Power Factor

    5 Gate Drive Voltage

    6 AC voltage

    7 Rail voltage

    8 Output voltage

    9 SOA(Safe Operation Area)

    10 Dynamic on-resistance

    11 Conduction losses

    12 Rush

    13 Ripple

    14 Saturation voltage

    15 Deskew

    16 Control loop stability

     

     

    Can you find any other items that need to test when we deal with Power Test?

     

  • 7. Re: Basic knowledge about power test
    leoglh2001 Level 7

    Ripple measurement:

    Ripple is a very small signal that exist in power supply, it will harm many sensitive operation parts in a automatic system. Such as in a train, process control and defense industry.

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