How to test the ripple coefficient of DC power supply with an oscilloscope
Open the Multisim simulation software, use the operational amplifier LM324 to build an adder circuit, superimpose the 5V voltage with the 50Hz small signal, and simulate the ripple
Add simulated devices such as resistors, capacitors, and power supplies, and connect them according to the adder circuit.
The capacitor C1 plays the role of blocking DC and passing AC. When using 5V DC, it will not be scaled and will directly follow the output at the output end.
For AC signals, they are output after scaling. The scaling ratio of high-frequency signals is 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 5V input voltage at the non-inverting terminal is isolated, and the AC 50Hz signal passes.
The -6dB cutoff frequency of this high-pass filter circuit is 1/(2πR1C1)=16Hz, 50Hz>>16Hz, so the impedance can be considered to be 0.
Connect the 5V DC power supply to the non-inverting terminal of the op amp, and input the AC signal Vs with an effective value of 100mV and a frequency of 50Hz at the inverting terminal.
According to theoretical analysis, the voltage at the output terminal of the op amp is 5-0.1*Vs (V)
Drag in the virtual oscilloscope, the protagonist of this video, and select the two-channel oscilloscope in the toolbar on the right.
Connect the two channels of the current indicator to the output end of the op amp at the same time. Channel A is used to observe the DC voltage, and channel B is used to observe the AC ripple. In order to facilitate observation, the color of the channel A connection is changed to light red, and channel B is used to observe the AC ripple. The line changes to light green, and the color of the waveform changes accordingly.
point
Click the "Run" button in the upper right corner to run the circuit, 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 AC coupling in AC coupling/DC coupling. Through the "AC coupling" function, only the AC signal is displayed. Adjust the zoom level of channel B. The reduction gear is 5mV/Div, that is, every 5mV. After isolating the DC 5V signal through "AC coupling" and adjusting the scaling 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.
Judging from the values measured by the cursor, the DC voltage measured by channel A is about 5V, while the peak-to-peak value of channel B is 26.897mV.
How to test the ripple coefficient of DC power supply with an oscilloscope
