How to measure the voltage ripple of DC switching power supply
Voltage ripple measurement:
The output voltage of 1.2V needs to be stable within a certain range, so there will be certain requirements for voltage ripple. Otherwise, if the ripple is too large, it will affect the operation of the subsequent circuit. Generally, the ripple is around 10% of the output voltage. For circuits that require high voltage accuracy, the smaller the ripple, the better.
So it becomes very important to confirm whether the voltage ripple is within our requirements, and the testing method is crucial. Different testing methods will result in different values, which can easily lead to misjudgments.
When measuring, the GND of the oscilloscope probe must be as close as possible to the GND of the output voltage. If it is too far away, it will bring in a lot of unnecessary interference, resulting in a larger ripple value. For example, if you use the grounding clip of an oscilloscope and clamp it on a distant GND (screw hole, mechanical housing, etc.), and place the oscilloscope probe at the output voltage position, the obtained value will not be the actual voltage ripple.
So how should we measure it?
1. Because voltage ripple belongs to the AC component, it is necessary to first adjust the oscilloscope to AC measurement mode.
2. Because the shortest contact distance between the GND of the oscilloscope probe and the GND of the voltage is required, a tool is needed. Some probes may come with this tool, while others can be made with wire.
3. After production, the oscilloscope was also adjusted. Taking the above buck voltage diagram as an example, the oscilloscope probe point is at the 1.2V position, and the wire is directly in contact with GND. That is to directly measure the ripple voltage at both ends of capacitor C401.
Inductive current measurement:
Current measurement is generally carried out using a current probe, as the current probe is an inductive measurement, it is necessary to first disconnect the circuit and then connect the circuit with a wire. The selected wires should be as short and thick as possible.
It is recommended to measure the inductance current on the side with a stable voltage. In a switching power supply circuit, the voltage on the power inductance side varies periodically, while the voltage on one side is a stable output voltage.
