Causes of harmonics in switching power supplies
Harmonic refers to a waveform of electricity with a higher frequency than the fundamental wave, usually originating from nonlinear loads, non sinusoidal voltages, electromagnetic interference, and other factors. The working principle of a switching power supply determines that it is prone to generating harmonics.
1. Short circuit effect of capacitor filter circuit
In switch mode power supplies, capacitor filtering circuits mainly reduce the pulsating voltage on the power output, but under high-frequency conditions, capacitors are also a type of short circuit. Short circuits can cause harmonic currents to flow into the power supply, causing oscillations in the conductor and resulting in noise and thermal effects.
2. Resonant effect of inductive filtering circuit
In switch mode power supplies, inductive filtering circuits are mainly used to prevent high-frequency fluctuations in power output. When the load current is very low, the inductance is in a resonant state, which will generate high-frequency harmonic currents. The high-frequency harmonic current generated will cause resonance in the power capacitor and line inductance, resulting in high-frequency oscillation when the current flows through.
3. The resonance effect of inductive feedback circuit
The resonant feedback circuit is an important performance feature of switching power supplies, which continuously monitors the load and power supply through a feedback controller to adjust the power output in a timely manner and improve the efficiency of the entire circuit. However, the inductive feedback circuit reduces the output voltage of the power supply through a resonant circuit, increasing the generation of harmonic currents.
4. The impact of working frequency
The higher the operating frequency of a switching power supply, the higher the harmonics and the richer the harmonic currents generated. High frequency current will generate relatively large electromagnetic waves on the coil, which will also lead to the phenomenon of mutual influence between the electrical appliances themselves and the electromagnetic waves in the air.
