Solution of light load howling of switching power supply
Switching power supply is a kind of high-frequency power equipment that can convert alternating current into direct current. In the development and application of power electronic technology, it is widely used in various electronic equipment, such as computers, communication equipment, industrial control and household appliances. However, the switching power supply will emit a kind of high-frequency noise called "howling" when it works, which affects the normal use and life of the equipment. Especially when the switching power supply is in a light load state, the noise is more obvious. This paper will introduce in detail the causes of light-load howling of switching power supply and how to solve it.
First, the cause of light load howling
When the switching power supply is working, its output voltage will change with the change of load size. Under normal circumstances, when the load current is at full load, the output voltage is relatively stable. However, when the load current is in a light load state, the output voltage becomes fluctuating, resulting in a high-frequency noise generator. This is because the switching elements can not be completely switched under light load, which leads to the increase of harmonics in the waveform of switching power supply, resulting in greater noise.
Second, the solution to the light load howling method
(A) optimize the design of switching power supply
Optimizing the design of switching power supply is one of the effective methods to reduce light load howling. In the design, the output voltage range of switching power supply should be set reasonably, the appropriate resonant capacitor should be selected, and some damping or filtering circuits should be added to prevent the generation of harmonics or reduce the spread of noise.
1. Set the output voltage range of switching power supply.
In the design of switching power supply, switching regulators and voltage regulators should be deployed, and the adjustment range of output voltage should be set reasonably, which can significantly reduce the noise. Usually, when adding regulators, attention should be paid to prevent poor load quality and waste of load voltage.
2. Choose a suitable resonant capacitor.
When the switching converter switches, the switching tube needs to be charged and discharged instantly, which will produce a large number of high-frequency signals on the frequency spectrum of the switching tube. At this time, appropriate resonant capacitors should be used for high-frequency filtering, so as to avoid problems such as flashing lights and wiring noise caused by high-frequency noise.
3. Add damping or filtering circuit.
Adding damping or filtering circuit in switching power supply can effectively reduce the noise of light load howling. Damping circuit is usually suitable for normal light load operation, and filter circuit is a more suitable method for switching power supply used in light load state. The filter circuit includes a low-pass circuit composed of LC, or adopts the method of combining AC power supply inductance to reduce the noise level of switching power supply.
(2) Optimize the power supply layout
The optimization of power supply layout is also an important means to solve the light load howling. Although noise can be reduced in the design and manufacture of switching power supply, other factors need to be considered to ensure the normal operation of switching power supply and reduce the noise level. At this time, the optimization of power supply layout will be very important.
1. Reduce the length of sensitive lines
When arranging power lines, the length of sensitive lines should be reduced as much as possible to prevent the influence of external electromagnetic interference (EMI). These circuits may include control circuits of switching devices, output voltage sampling circuits, power supply circuits and load circuits.
2. Pay attention to signal grounding
For some special application scenarios, some signal transmission and processing lines need to be grounded. In order to minimize the noise level of light-load howling, signal grounding should be separated from power grounding to avoid mutual interference at the grounding point of transmission lines.
(C) improve the power load
Improving power supply load is an effective method to solve the problem of light load howling. High-power load or suitable compensation circuit can be used to improve the power supply load under light load. When the load current is in the minimum or light load state, it is an effective method to use high-power load. Because under high load current, the impedance of power supply load is low, and the adjustment and stability of power supply are good; However, under light load current, the load impedance increases, the adjustment ability of power supply weakens and the noise level increases. The staggered circuit can reduce the fluctuation of power supply load and improve the load condition under light load, thus reducing the noise level.
