The Causes of Harmonic Generation in Switching Power Supplies
In modern electronic equipment, switching power supply is a widely used form of power supply, which has the characteristics of small size and high efficiency. However, switching power supplies can also generate harmonics, which to some extent affect the quality of the power supply and the stability of the power grid, and even pose a threat to circuits and devices. Therefore, it is imperative to solve the harmonic problem of switching power supply.
Harmonics refer to an electrical waveform with a higher frequency than the fundamental wave, typically originating from factors such as nonlinear loads, non sinusoidal voltage, and electromagnetic interference. The working principle of a switching power supply determines its susceptibility to harmonic generation.
1. Short circuit effect of capacitor filtering circuit
In switching power supplies, the capacitor filtering circuit mainly plays a role in reducing 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 causing noise and thermal effects.
2. Resonance effect of inductance filtering circuit
In switching power supplies, the inductance filtering circuit is mainly used to prevent high-frequency fluctuations in the output of the power supply. 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, causing high-frequency oscillation when the current flows through.
3. Resonance effect of inductance feedback circuit
Resonant feedback circuit is an important performance characteristic of switching power supply, which continuously monitors the load and power supply conditions through a feedback controller, in order to adjust the power output in a timely manner and improve the efficiency of the entire circuit. However, the inductance 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 more abundant the harmonic currents generated. And 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 appliance itself and the electromagnetic waves filled with air.
