The role of oscilloscope recording length in power supply measurement
The ability of an oscilloscope to capture events over a period of time depends on the sampling rate used and the depth (record length) of the memory in which the sampled signal is stored.The memory filling rate is proportional to the sampling rate.If the sampling rate is set very high to provide detailed high-resolution signals, the memory will fill up quickly.
For many SMPS power measurements, a quarter or half cycle (90 or 180 degrees) of the power signal must be captured, or even the entire cycle.This is to accumulate enough signal data to offset the power frequency voltage fluctuations in the calculation.
Identify the real Ton and Toff conversions
In order to determine the loss accurately, the oscillations in the switching signal must be filtered first.Oscillations in switching voltage signals can easily be mistaken for switching on or off.The large oscillations are caused by parasitic elements in SMPS circuits that switch between non-continuous current mode (DCM) and continuous current mode (CCM).