How to Avoid Interference in Switching Regulated Power Supplies
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 an instantaneous fluctuation in the grid voltage or load, the regulated power supply will compensate for the voltage amplitude at a response speed of 10-30ms, making it stable within ± 2%.
Switching regulated power supply is a relatively new type of power supply. It has the advantages of high efficiency, light weight, ability to increase or decrease voltage, and high output power. However, due to the circuit working in the on/off state, the noise is relatively high. Using the following diagram, we will briefly explain the working principle of a step-down switching power supply. As shown in the figure, the circuit is composed of switch K (triode or Field-effect transistor in the actual circuit), Flyback diode D, energy storage inductance L, filter capacitor C. When the switch is closed, the power supply supplies the load through the switch K and inductor L, and stores some of the electrical energy in the inductor L and capacitor C.
When the switching regulated power supply works, the switching triode and the Flyback diode (or another switching triode) are always turned on or off alternately. KQ and KD are not ideal devices, and the transition between the two states takes a certain time, which results in spike interference. During the state transition process, the conducting switch is not fully conducting, while the cut-off switch has no cut-off moment. There is a direct path from the power supply to the ground, generating transient current Is. This current is related to factors such as the difference between the current Imax when the switch transistor is on and the current Icmin when it is off, as well as the duration of simultaneous conduction of switches KQ and KD. Due to the influence of circuit distribution parameters, ringing oscillation occurs on the waveform.
The switch regulated power supply radiates interference into space during operation. The level of radiated noise is inversely proportional to the distance from the radiation source. Generally, wiring can be done at a distance of 5cm. 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 the electromagnetic coupling between the input and output lines, they must be kept away.
