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Can switching power supplies replace low frequency transformers?
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- Time of issue:2020-08-03
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Can switching power supplies replace low frequency transformers?
Can switching power supplies replace low frequency transformers?
1. The low-frequency transformer will not be replaced;
2. The low-frequency transformer has no pulse interference of switching power supply;
3. The low-frequency transformer can isolate various grid pulse interference;
4. The low-frequency transformer has the anti-surge ability that the switching power supply cannot resist, especially the lightning;
5. The linear power supply made of low-frequency transformer has the best ripple-inducing performance;
6. Low-voltage switch chips can be used at the output of the low-frequency transformer, which has isolation and high efficiency;
In industry, low-frequency transformers can well isolate the interference caused by various high-power frequency conversion, servo, and SCR phase control.
The difference between switching power supply and transformer
Switching power supplies and transformers have a wide range of uses, and they also have different differences, both in function and use. Simply put, a transformer is an electronic component on a circuit, while a switching power supply is a circuit composed of multiple electronic components that can realize the corresponding electric energy conversion. Their differences can be distinguished from function and purpose. Refer to the following figure:
Can switching power supply replace low frequency transformers? Talking about transformers under switching power supply
1. The functional difference between switching power supply and transformer
1. The switching power supply is DC-DC, and the transformer is AC-AC;
2. The working frequency of the switching power supply is relatively high (usually tens of kilohertz), and the transformer has high frequency and low frequency. The pulse transformer used in the switching power supply is a high frequency transformer, and the iron core is a magnet such as ferrite. The core is small in size and high in efficiency (the higher the frequency, the higher the efficiency). When it comes to transformers, the first thing that everyone thinks of is a power frequency transformer. Its operating frequency is 50 Hz, which is a low-frequency transformer. Its core must be made of soft magnetic materials. Stacked silicon steel sheets (to prevent eddy current from generating Joule heat);
3. The functional categories of the two are not the same. The switching power supply includes a pulse transformer, and also includes the upper and lower rectifier parts, and no matter which frequency range the transformer is just transforming, it has no rectification function;
4. Switching power supply: Compared with traditional power supply, it has the characteristics of low power consumption, high efficiency, small size, light weight and wide voltage regulation range. It is widely used in the fields of computer and peripheral equipment, communication, automatic control, household appliances and so on. But the outstanding shortcoming of the switching power supply is that it produces strong electromagnetic interference. The interference signal has a wide frequency range and a certain amplitude. It will pollute the electromagnetic environment through conduction and radiation, and cause interference to communication equipment and electronic products. If not handled properly, the switching power supply itself will become a source of interference.
Traditional transformer power supply: The disadvantage is that it is heavy in size and low in efficiency. However, in order to pursue profit, manufacturers in the market use low-quality selenium steel sheets or fake ones, which causes transformers to overheat and lower efficiency.
2. What is the difference between switching power supply and transformer in use?
Switching power supply: The switching power supply can stably convert the voltage within a certain range to a very accurate low or high voltage (for example, 110V-250 input, the output voltage can be stably controlled at the required voltage plus or minus 0.5v).
Transformer: The output voltage of the transformer changes continuously with the input voltage, that is, the input voltage increases and the output voltage increases, and the input voltage decreases and the output voltage decreases.
In summary, it can be concluded that the switching power supply first converts alternating current into direct current, and the direct current is transformed into a higher frequency alternating current through the power switch tube. The voltage conversion through the high frequency transformer not only improves the efficiency, but also greatly reduces the size after the high frequency. , It also saves copper and iron losses. Because it is controlled by the power switch tube, the switching tube conduction time is short when the current is small, and the output voltage is only required. When the load is large, the switch tube keeps working to maintain the output voltage. Therefore, the output voltage of the switching power supply is stable and can be used as a high-precision instrument such as an LED display.
In summary, the current application range of switching power supply is more extensive, and it is more suitable for market demand. After understanding the difference between switching power supply and transformer, I also hope that all manufacturers of switching power supply can do a good job of quality control. Interests harm the interests of customers.
Causes of howling in switching power supplies and transformers
There are four main reasons for the howling of the switching power supply transformer: the process problem of the transformer, the loop problem of the transformer, the core problem of the transformer and the load problem of the switching power supply, which are analyzed one by one below.
(1) Process problem of transformer
①The dipping paint is not dried in place, which causes the magnetic core to be weak, causing mechanical vibration and noise;
②The length of the air gap is not suitable, which causes the transformer to be unstable and make noise;
③The anchor point can cause noise if the wire package is not tightly wound;
④ The magnetic core combination has an air gap, which causes air vibration at high frequencies and makes noise (if the transformer is fully immersed in vacuum, it will generally not make a sound).
(2) The loop problem of the transformer
The loop problem of the transformer means that the loop of the transformer oscillates, which causes the transformer to whistle.
①Improper wiring of the circuit board, causing interference to cause oscillation, resulting in noise;
②Improper setting of feedback loop parameters causes the loop to be unstable and cause oscillation and noise;
③Quality problems of components in the loop, such as insufficient input filter capacitor capacity, poor quality output rectifier fast recovery diodes, poor quality power MOS tubes, poor quality of high-voltage capacitors or diodes in the RCD recoil absorption loop, etc. Problems may cause vibration and noise.
(3) The core problem of the transformer
When the transformer core is saturated, the current in the coil increases, the transformer heats up and generates self-excited oscillation, and the oscillation of the coil causes the surrounding air to vibrate and make noise.
(4) Load problem of switching power supply
① In the case of no load or light load, the switching power supply will oscillate at certain operating points, which is manifested as the howling of the transformer and the unstable output.
This phenomenon occurs because the instantaneous turn-on time of the switch is too large when there is no load/light load, which causes the output energy to be too large, and the voltage overshoot is also large, and it takes a long time to recover to the normal voltage, so the switch needs to stop working For a period of time, the switch works in the intermittent working mode, causing the transformer to vibrate at a lower frequency (a regular intermittent full cut-off period or a frequency where the duty cycle changes drastically).
②The transformer is working in a severe overload state, and it may be burnt at any time-this is the origin of the "screaming" before the burning of many power supplies.
Switching power supply transformer detection method
(1) Visual inspection. The switching power supply transformer has a high operating frequency of 15625 Hz. Magnetic materials are generally used to conduct magnetism. The common fault is leakage or short circuit between windings. During the inspection, first observe whether there are traces of burning and scorching, whether the appearance is too dirty, and whether there is dirt between the pins (some switching power supply transformers have very small spacing between the pins, such as the Sanyo 83P movement switching power supply transformer), Because the switching power supply transformer is installed close to the printed circuit board, it is easy to accumulate dust, and it is easy to discharge and ignite when it encounters the weather or the environment is humid.
(2) Multimeter test. There is no problem with the appearance of the switching power supply transformer. Use a multimeter to measure the resistance value to determine whether the coil has an open circuit fault. The switching power supply transformer with severe short circuit can also be measured with a multimeter. When measuring, you can select an appropriate resistance file to make the measured resistance value near the median value. According to the number of turns of the winding and the wire diameter used, you can find out each enameled wire Meter ohm value. Calculate the ohm value of the winding and compare it with the measured resistance value to determine whether there is a short circuit, but this is only a rough measurement. Some switching power transformers have resistance due to inter-turn insulation breakdown or inter-layer insulation breakdown. If the values are similar, they may not be able to be measured.
The insulation resistance between each winding of the switching power supply transformer is infinite, and the insulation resistance between each winding and the magnetic core (iron core) should also be infinite.
(3) Alternative measurement. If you have a switching power supply transformer of the same specification, you can use the alternative test, which is intuitive and easy. Hope it helps you
Professional transformer, inductor manufacturer
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