How to avoid interference with switching regulated power supply
A stabilized voltage supply is an electronic device that can provide stable AC or DC power to a load, including two categories: AC stabilized power supply and DC stabilized power supply. When there is a momentary fluctuation in the voltage or load of the power grid, the regulated power supply will compensate for the voltage amplitude with a response speed of 10-30ms, stabilizing it within ± 2%.
Switching stabilized power supply is a relatively new type of power supply. It has the advantages of high efficiency, light weight, adjustable voltage, and high output power. However, due to the circuit operating in a switch state, the noise is relatively high. Through the following diagram, let's briefly explain the working principle of a step-down switching power supply. As shown in the figure, the circuit consists of switch K (in actual circuits, it is a transistor or field-effect transistor), freewheeling diode D, energy storage inductor L, filtering capacitor C, etc. When the switch is closed, the power supply supplies power to the load through switch K and inductor L, and stores some of the electrical energy in inductor L and capacitor C.
During the operation of a switch mode power supply, the switching transistor and freewheeling diode (or another switching transistor) always alternate between conduction and cutoff. KQ and KD are not ideal devices, and the transition between the two states requires a certain amount of time, resulting in spike interference. During the state transition process, if the switch that is supposed to conduct is not fully conductive, and the switch that is supposed to be turned off is not turned off at the moment, there is a direct path from the power supply to the ground, generating a transient current Is. The current is related to factors such as the difference between the current Imax when the switching transistor is turned on and the current Icmin when it is turned off, as well as the duration of the simultaneous conduction of switches KQ and KD. Due to the influence of circuit distribution parameters, ringing oscillations appear on the waveform.
The switch stabilized power supply radiates interference to the space during operation. The level of radiated noise is inversely proportional to the distance from the radiation source. Generally, wiring should be done at a distance of 5cm or more. If it is not allowed structurally, shielding should be added. A strong electromagnetic field is generated around the power input line, and in order to reduce electromagnetic coupling between the input and output lines, they must be kept away from each other.
