How to test DC power supply ripple factor with an oscilloscope
I designed an analogue circuit using multisim software and simulated measurements using a virtual oscilloscope.
You can refer to the video to measure the ripple factor of a DC power supply.
The specific steps are as follows:
Open the Multisim simulation software, use the op-amp LM324 to build the addition circuit, superimpose the 5V voltage with the 50Hz small signal to simulate the ripple
Add resistors, capacitors, power supply and other simulation devices, and according to the adder circuit wiring
One of the capacitor C1 plays the role of blocking DC and AC, using 5V DC is not deflated, and follows the output directly at the output.
For AC signals, it is through the op-amp scaling after the output, high-frequency signal scaling ratio of R2/R1, that is, the output amplitude is reduced to 0.1.
Resistors C1 and R1 form a high-pass filter circuit, so that the input voltage 5V at the in-phase end is isolated, while the AC 50Hz signal passes through.
The -6dB cutoff frequency of this high-pass filter circuit is 1/(2πR1C1) = 16Hz, and 50Hz >> 16Hz, so the impedance can be considered to be 0.
A 5V DC power supply is connected to the in-phase end of the op-amp, and an AC signal with an RMS value of 100mV and a frequency of 50Hz is input to the inverted end, Vs.
According to theoretical analysis, the voltage at the output of the op-amp is 5-0.1*Vs (V).
Drag in the protagonist of this video - the virtual oscilloscope, and select the two-channel oscilloscope in the right toolbar.
Connect the two channels of the oscilloscope to the output of the op-amp at the same time, channel A is used to observe the DC voltage, channel B is used to observe the AC ripple. In order to facilitate the observation, the colour of the channel A connection is changed to light red, and the channel B connection is changed to light green, and the colours of the waveforms will be modified accordingly.
Click the "Run" button at the upper right corner to run the circuit, and double-click the "Oscilloscope" icon to open the "Oscilloscope Display Window".
On the oscilloscope display window, adjust the zoom level of channel B. The most important thing is to click on the AC coupling / DC coupling in the cross-wave coupling through the "AC coupling" function, which only displays the AC signal, adjust the zoom level of channel B 5mV / Div, i.e., 5mV every 5mV. After isolating the DC 5V signal by "AC coupling" and adjusting the zoom level to 5mV/div, we can clearly observe the ripple.
Move the two cursor positions on the "Oscilloscope" to test the voltage of channel A and channel B;
Move cursor 1 to the peak position of channel B, and move cursor 2 to the trough position of channel B.
From the values measured by the cursors, the measured DC voltage for channel A is approximately 5V, while the peak-to-peak value for channel B is 26.897mV.
