Possible source of noise
< br >
The most common noise source in flyback power supplies is the noise element. This noise is usually generated by ceramic capacitors or ferrite transformer cores. Noise in ceramic capacitors is usually caused by the reverse piezoelectric effect. When a voltage is applied to the medium structure, mechanical stress or strain will be induced, resulting in material deformation. When this material is deformed, it expels the surrounding air, resulting in noise.
< br >
Because the reverse piezoelectric effect occurs when large voltage swings occur, designers can focus on ceramic capacitors with high dV\/dt swings. In a typical power supply, these capacitors include buffer capacitors, clamp capacitors, and ceramic output capacitors. To quickly determine if a ceramic capacitor is producing noise, replace it with a metal film capacitor with the same capacitance value and the appropriate voltage rating. If the noise level drops, you have found the source of the noise in the circuit.
< br >
If the noise source is a clamped capacitor, it can be completely replaced with a metal film capacitor, or try to use a ceramic capacitor with a different dielectric material. Another method is to replace the clamping capacitor in use, for example, by replacing it with a regulator clamp circuit. If the noise problem is from the buffer capacitor, it can be replaced with a metal film capacitor, or the value of the series resistance can be increased to reduce the dV\/dt noise on the capacitor. You can also use ceramic capacitors of other media to see if the noise can be reduced.
< br >
Manage transformer core noise
< br >
On the other hand, the noise generated by the transformer core is usually caused by magnetostriction, which is similar to the reverse piezoelectric effect. Many ferromagnetic materials change shape when affected by a magnetic field. As the magnetic field in the transformer core changes, such materials will cause the core to physically vibrate. When the vibration frequency reaches the mechanical resonance frequency of the transformer, the vibration will be amplified and cause greater audio noise. In AC electrical equipment, such as transformers that use a 60Hz external magnetic field, the maximum length change occurs twice per cycle, resulting in the familiar 120Hz noise.
< br >
If you have this problem with your design, make sure it is not caused by improper design before you start investigating the cause. First, verify that the supplied input voltage and output load meet the design specifications. If the operating voltage of the power supply is lower than the specified minimum input voltage, or higher than the specified output load, then part of the AC cycle will lose voltage regulation, which will cause the magnetic flux in the core to increase and generate noise.
< br >
If the input voltage and load are within the specification range, then verify that the value of the input large capacity capacitance is correct. If the input capacitance is too small relative to the application, the DC bus voltage will decrease significantly between AC refresh cycles, causing the AC cycle of some inputs to lose voltage regulation.
< br >
Transformers contain a variety of movable components, such as coils, isolation tapes and skeletons, which make transformers a common source of noise. The current in the coil can generate an electromagnetic field, which creates forces that cause mechanical vibration in many transformer components. The most effective way to reduce the physical movement of transformer components is to use bonding materials or paint. For example, impregnating a magnetic core with varnish is a widely used method to prevent the core from vibrating with the skeleton. Although there are many coating technologies available from suppliers, we recommend using varnish impregnation technology rather than vacuum impregnation because vacuum impregnation can significantly increase the winding capacitance, which reduces efficiency and increases EMI.
< br >
If your design requires the use of a long core type transformer, another strategy you can use is to use standard core lengths. Long core products, such as EEL transformers and EERL transformers, have very low mechanical resonant frequencies. This low resonant frequency tends to increase audio noise. Using a standard core length with a higher resonant frequency can alleviate this problem. However, it is important to note that if you switch to a shorter standard core, you must use a larger core size to provide sufficient winding window area.
< br >
If the noise problem exists in the ceramic output capacitor, many different strategies can be tried to solve it. One way is to try to replace electrolytic capacitors or replace capacitors with other dielectric materials. Alternatively, the problem capacitor can be replaced with multiple parallel ceramic capacitors. A reduction in the size of each capacitor will result in a corresponding reduction in its surface area, changing the mechanical resonance of the capacitor.
< br >
Processing pulse beam
< br >
Pulse beams are another potential source of noise. The pulse beam phenomenon occurs when the conducted current pulses in the design are clustered together and then a larger number of jump pulses are present. Pulse aggregation produces frequency components in the switching mode, which are usually in the auditory range. Pulse beams are most common in power supplies that use an on\/off control mode.
< br >
To determine if this phenomenon exists in your design, disconnect the MOSFET drain wiring and then insert a current loop to monitor the switching pattern of drain current.
< br >
Usually, the pulse beam phenomenon indicates that the feedback circuit is too slow, causing the controller response to lag. To diagnose this problem, you can first verify that all the component values in the feedback circuit match the values specified in the design. One possible solution is to use a D-type optocoupler in the design. The Type D optocoupler has a higher gain than the standard optocoupler. Another strategy is to add a feedback loop acceleration circuit to reduce response time. This circuit will ensure that the optocoupler transistor is always operating in the active region, which prevents it from saturating and improves response speed.
The answer is as follows: 1. Add a filter capacitor: Add an appropriate capacitor between the positive and negative terminals of the power output to effectively reduce noise.
2. Select high-quality components: Select high-quality capacitors, inductors and other components, which can effectively reduce the generation of noise.
3. Increase shielding: Add some metal shielding cover near the lead line of the power supply to effectively isolate the noise.
4. Optimize PCB layout: Optimize PCB layout to minimize the cross of signal lines and avoid signal interference.
5. Use digital control chips: Digital control chips can effectively reduce noise because they can digitally control the output voltage and current.
6. Reduce the switching frequency: Properly reduce the switching frequency, which can reduce the generation of noise. However, it should be noted that too low a frequency will affect the efficiency of the power supply.
There is a sizzling noise, generally the lamp head circuit is damp, can dry for a period of time and then use, may be solved.
< br >
It may also be that there is a problem with the electronic components on the circuit such as the starting capacitor or the transistor, and some may be nearing the end of their life, so it will be like this.
< br >
If it is the electronic components to be broken, it needs to replace the bulb, these components if burned light light is not bright, serious will lead to a short circuit in the home, the leakage protection in the home will trip, so as long as there is a sizzle, and accompanied by the light flickering situation, it is recommended to replace in time.
The LED driver has noise, which indicates that the output power does not match the rated power of the drive itself. You are advised to adjust the power of the light source. Just match the driver.