How to avoid interference in switching regulated power supply
Switching stabilized voltage supply (stabilized voltage supply) is an electronic device that can provide stable AC or DC power to the load, including AC stabilized power supply and DC stabilized power supply. When the grid voltage or load fluctuates momentarily, 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, ability to increase and decrease voltage, and high output power. However, since the circuit works in a 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 consists 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 (it can also be another switching transistor) are always turned on or off alternately. KQ and KD are not ideal devices. The conversion of the two states takes a certain amount of time. This is Spike interference occurs. During the state transition process, the on switch is not completely turned on, and the off switch does not turn off at the moment. There is a direct path from the power supply to the ground, resulting in a transient current Is. This current is related to the difference between the current Imax when the switching transistor is turned on and the current Icmin when it is turned off, the duration of the simultaneous conduction of switches KQ and KD, and other factors. Due to the influence of circuit distribution parameters, ringing oscillation appears on the waveform.
The switching regulated power supply radiates interference into space when it is working. Radiated noise level is inversely proportional to the distance from the radiation source. Generally, wiring can be done 5cm away. If the structure does not allow it, shielding should be added. 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 kept away from each other.
