How to overcome the interference of switching power supply
Suppression of radiation disturbanceElectromagnetic radiation harassment refers to by any member, antenna, cable or cable radiation.In general, the input and output DC sockets (including leads) shall be separated and removed as far as possible in the layout of the circuit components. Using one end input, the other end output is a reasonable layout. But considering the internal heat radiation ventilation, the power supply adopts the heat radiation structure of Fig. 2. The unavoidable problem is that space coupling may occur between the input and output cables, which produces strong radiation when high frequency conduction currents pass through.
Suppression of conduction disturbanceThe main source of the transmitted noise is the half bridge converter. The power switching tubes S1 and S2 are alternately operated at frequency 25 kHz, the collector of the power switch, the emitter voltage Uce and the emitter current,. The waveform is close to the square wave. Fu Liye analysis shows that the rectangular wave pulse has a fairly wide frequency bandwidth and is rich in higher harmonics, and the spectral amplitude of the pulse waveform is higher in the low frequency range. In addition, when the power switch tube is in the cut-off period, the current variation caused by the leakage inductance of the high-frequency transformer winding will also cause peak interference.
Suppression of harmonic currentsPower factor correction can solve the problem of excessive harmonic current. Active power factor correction using Boost boost PFC circuit, power factor is increased to more than O.99, the harmonic current is very small, but the circuit is complex, the cost is not low, and switching noise in the circuit switch and high voltage rectifier diode will become a new source of harassment, so that the EMI standard to increase the difficulty.
EMI testThe values of the 7~21 harmonic currents listed in Table L show that the 11, 15 and 17 harmonic currents exceed the standard values.The results of radiation disturbance prediction exceed the limit at 30 ~ 50MHz and 100MHz, as shown in figure 4.
With the continuous development and maturity of switching power supply technology, the demand for switching power supply is increasing in various application fields. However, there are serious electromagnetic interference (EMI) problems in switching mode power supplies. It not only causes pollution to the power grid, but also directly affects the normal work of other electrical appliances. As a result of radiation interference, it breaks into the space and causes electromagnetic pollution to the space. Thus, the electromagnetic compatibility (EMC) problem of the switching power supply is produced. Electromagnetic compatibility (EMC) refers to the ability of a device or system to function properly in its electromagnetic environment and that it does not constitute an electromagnetic disturbance that cannot be contained in the environment.
