Unstable waveform

梅花飘落孤人醉

Unstable waveform [Copy link]

I have a question. A circuit is powered by DC and a waveform can be displayed on an oscilloscope, but the waveform is unstable. Is it a problem with the filter circuit?

maychang

"I have a circuit with DC power supply. The waveform can be displayed on the oscilloscope, but the waveform is unstable."

You have to make it clear at which point in the circuit the waveform appears, right?

"The waveform is unstable", what does it mean? Post the waveform for everyone to see.

qwqwqw2088

Whether the DC power supply is stable or not depends on the load change and ripple

The load change causes the output to change too much, which is unstable.

The output has many AC components, the ripple is relatively large and unstable

These are all things that require test data.

梅花飘落孤人醉

maychang published on 2020-9-14 10:15 "I would like to ask if a circuit with DC power supply can display a waveform on the oscilloscope, but the waveform is unstable." It is always necessary to make it clear which part of the circuit is...

I want to post the circuit diagram and waveform diagram, but I don't know why I can't upload the picture. The waveform is unstable. It can be seen that it is a sine wave, but the waveform jumps up and down and shakes.

梅花飘落孤人醉

Plum blossoms fall and lonely people get drunk Published on 2020-9-14 17:20 I want to post the circuit diagram and waveform diagram, but I don’t know why I can’t upload the picture. The waveform is unstable and it can be seen that it is a sine wave, but the waveform is up and down...

After the repair, the capacitance of the filter capacitor was changed, and some filter capacitors were removed. I didn't understand why I did this, but the master said to do it this way.

chunyang

Plum blossoms fall and lonely people get drunk Published on 2020-9-14 17:20 I want to post the circuit diagram and waveform diagram, but I don’t know why I can’t upload the picture. The waveform is unstable and it can be seen that it is a sine wave, but the waveform is up and down...

The original poster should also give the specific circuit and explain the measurement points.

qwqwqw2088

Plum blossoms fall lonely drunk published on 2020-9-14 17:20 I want to post the circuit diagram and waveform diagram, but I don't know why I can't upload the picture. The waveform is unstable and it can be seen that it is a sine wave, but the waveform is up and down...

In the reply box, click Advanced Mode, and then click on the picture to upload the picture.

梅花飘落孤人醉

The measurement points are the measurement points above C20 and C21, and the capacitors of C20 and C21 are removed. I dare not give more details about the specific circuit, and the waveform diagram cannot be taken now.

guyanqiu

You can simulate it. The filter circuit also has phase shift. If the phase shift exceeds 360 degrees and the circuit gain is greater than 1, it will oscillate. Therefore, if you remove some capacitors or add some capacitors to reduce the phase shift, there will be no problem. When simulating, you can use AC analysis.