How to solve the problem of large power output ripple?

Aguilera

How to solve the problem of large power output ripple? [Copy link]

 

As shown in the figure, how to solve the problem of large power output ripple? How to reduce the PKPKP value? Does anyone have a good idea?

maychang

Your 9V DC output is one of the two outputs of the flyback switching power supply, which is obtained by linear voltage regulation at the Q1 stage and then by linear voltage regulation at the VR1 stage. The circuit is quite special, and I don't know why such a complicated circuit is used.

maychang

The 1.5V peak-to-peak ripple is indeed very large, especially after two stages of linear regulation, there should not be such a large ripple.

Guess 1: The component layout is unreasonable, especially the ground wire layout is unreasonable.

Guess 2: The measurement method is unreasonable. The peak-to-peak value estimation was measured using an oscilloscope, which introduced the magnetic field noise of the flyback switching power supply transformer.

maychang

Since the ripple is measured with an oscilloscope,

First, check whether the ripple frequency is the same as the PWM operating frequency of the flyback switching power supply.

Second, clamp the oscilloscope ground clamp at pin 1 of VR1, and measure the ripple at the VR1 input (pin 2), Q1 collector, and D4 cathode respectively.

There is no simple way, we can only measure at multiple locations and then analyze.

maychang

Even the oscilloscope ground clip can be clamped on pin 1 of VR1, and the probe can be touched to pin 11 of the flyback transformer to see how big the ripple value is. The purpose of this measurement is to determine whether the ground resistance is too large and introduces ripples, or whether the oscilloscope ground clip forms a loop and introduces ripples.

不亦心

There is too little information, so I can only count on my fingers. Have you seen the C10 and C11 waveforms?

qwqwqw2088

The ripple size is related to the inappropriate input and output capacitance of VR1d

Nubility

Stack capacitors, put a bunch of large capacitors at the output end, and then the power supply will start slowly

Nubility

At least we need a full-wave rectifier, and at least we need a DCD chip with a relatively high switching frequency.

chunyang

How did you measure it? I suspect there is something wrong with the test method. The output of the linear regulator should not have such a large ripple. Please post the specific measured waveform.

led2015

Does the capacitance value matter? Adding appropriate filter capacitors at the output of the power supply can effectively reduce ripple. The filter capacitor can absorb high-frequency noise and maintain the stability of the power supply output.

Aguilera

Nubility posted on 2023-9-22 15:39 Stack capacitors, put a bunch of large capacitors at the output end, and then the power supply has a slow start

Where is the stack capacitor added?

Can I add magnetic beads and ceramic capacitors?

Nubility

Aguilera posted on 2023-9-27 13:40 Where should the stack capacitor be added? Can magnetic beads and ceramic capacitors be added?

The only way to reduce the ripple is to increase the capacitance at the output end, but this will result in a very high startup current. Your circuit has a big problem. At least full-wave rectification and a high-frequency DCDC chip are needed to achieve small ripple.

ardtek

C17 is replaced with 10UF. What a good electronic filter structure. Make the best use of it.