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
Using LeCroy oscilloscope, we can test power as shown in below picture,
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.
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.
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
14 Saturation voltage
16 Control loop stability
Can you find any other items that need to test when we deal with Power Test?
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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