How to avoid interference of switching regulated power supply
Switching regulated power supply (stabilized voltage supply) is an electronic device that can provide stable AC or DC power for the load, including AC regulated power supply and DC regulated power supply. When the grid voltage or load fluctuates instantaneously, the regulated power supply will compensate the voltage amplitude with a response speed of 10-30ms to stabilize it within ±2%.
Switching regulated power supply is a relatively new type of power supply. It has the advantages of high efficiency, light weight, step-up and step-down, and large output power. However, since the circuit works in the switching state, the noise is relatively large. Through the figure below, let's briefly talk about the working principle of the step-down switching power supply. As shown in the figure, the circuit is composed of switch K (transistor or field effect transistor in the actual circuit), freewheeling diode D, energy storage inductor L, filter capacitor C, etc. When the switch is closed, the power supply supplies power to the load through the switch K and the inductor L, and stores part of the electric energy in the inductor L and the capacitor C.
When the switching regulated power supply is working, the switching transistor and the freewheeling diode (or another switching transistor) are always turned on or off alternately. KQ and KD are not ideal devices, and the transition between the two states takes a certain amount of time, which is Interference spikes are generated. During the state transition process, the switch that is turned on is not completely turned on, and the switch that is turned off is not turned off at the moment, there is a direct path from the power supply to the ground, and a transient current Is is generated. This current is related to factors such as the difference between the current Imax when the switch transistor is turned on and the current Icmin when it is turned off, and the duration of simultaneous conduction of the switches KQ and KD. Due to the influence of circuit distribution parameters, ringing oscillations appear on the waveform.
When the switching regulated power supply is working, it radiates interference to the space. The radiated noise level is inversely proportional to the distance from the radiating source. Generally, it can be wired outside 5cm. If the structure is not allowed, it should be shielded. A strong electromagnetic field is generated around the power input line. In order to reduce the electromagnetic coupling between the input line and the output line, the two must be far away.
