How to measure the ripple voltage of variable frequency power supply?
By measuring the operating voltage and current, it is possible to determine the effect of the application on the associated electronic components and the cause of problems in the control circuits. When the frequency conversion power supply is in use, when the working voltage or current is too high and exceeds the standard range, dangerous accidents are likely to occur. Therefore, it is more and more necessary to measure the operating voltage and monitor the value change of the operating voltage. Next, the whole process for measuring the ripple voltage of the variable frequency power supply will be introduced in detail.
1. You can first use a digital oscilloscope to acquire all the waveforms, and then zoom in on the waveforms for observation and measurement (both automatic and cursor measurements are available), and you also need to use the FFT function of the digital oscilloscope to perform operations from frequency domain analysis. Bandwidth limiting is often used to indicate ripple, so to avoid picking up high frequency noise that is not actually there, set the correct bandwidth limit for the digital oscilloscope being used for measurements.
2. Remove the probe cap and combine to form an oscilloscope. This eliminates the antenna formed by the long ground cable. Wrap a small piece of wire around the ground point of the probe and connect the ground wire to the power supply. In this way, the length of the tip exposed to high electromagnetic radiation around the power unit can be shortened, further reducing the amount of pickup.
3. In the isolated variable frequency AC power supply, a large amount of common mode current will flow through the ground point of the probe, and there is a voltage drop between the ground point of the power supply and the ground point of the digital oscilloscope, which can be expressed as ripple. To avoid this problem, special attention should be paid to common-mode filtering in the power supply design.
4. Also, wrapping the digital oscilloscope leads around a ferrite core helps minimize such currents and creates a common mode inductor. It does not interfere with the measurement of differential operating voltages and reduces the chance of data errors caused by common-mode currents.
5. After integrated into the system, the power ripple performance may be improved. In most cases, there will be some inductance between the variable frequency AC power supply and the other components of the system. This inductance can exist in the wiring or it can be etched into the board. There are always additional bypass capacitors around the chip which represent the load for the power supply unit. Together they form a low-pass filter that further reduces power supply ripple or high-frequency noise.
6. Also, in the special case where current flows for short periods of time through a one-inch conductor of a 15nH inductor and a 10F bypass capacitor, this filter has a cutoff frequency of 400kHz. In this case, the high-frequency noise is greatly reduced, and the cutoff frequency of the filter is lower than the ripple frequency of the power supply, so the ripple can be greatly reduced.
7. The DC voltage output from the power supply should be a fixed value, but in most cases, after the AC voltage is rectified and filtered, there will be more or less residual AC components, including periodic and random components of interference signals called It is ripple, large ripple will affect normal CPU and GPU operation, the smaller the value, the better.
The above is the specific measurement process of the ripple voltage of the variable frequency power supply. Ripple voltage actually refers to the power frequency AC component contained in the DC output voltage, which will affect the life of the capacitor and the quality of the output voltage, and requires special attention, because it will affect the effectiveness of the applied force. Also, when using a digital oscilloscope, care must be taken to ensure that the device is operated within a safe area to ensure the safety of the device and the operator.
