How to solve the ripple harmonic and noise interference generated by the regulated power supply
ripple
Ripple: It is a clutter signal containing periodic and random components attached to the DC level. It refers to the peak value of the AC voltage in the output voltage under the condition of rated output voltage and current. Ripple voltage in a narrow sense refers to the power frequency AC component contained in the output DC voltage.
Noise: For the nominal noise in electronic circuits, it can be generally considered that it is a general term for all signals other than the target signal. At first, people called the electronic signals that caused the noise emitted by audio equipment such as radios as noise. However, the consequences of some non-purpose electronic signals on electronic circuits are not all related to sound, so people gradually expanded the concept of noise. For example, those electronic signals that cause white stripes on the screen are also called noise. It can be said that all signals in the circuit except the target signal, regardless of whether it affects the circuit or not, can be called noise. For example, ripple or self-oscillation in the power supply voltage can adversely affect the circuit, causing the audio device to hum or cause the circuit to malfunction, but sometimes it may not cause the above consequences. For this kind of ripple or oscillation, it should be called a kind of noise of the circuit. There is also a radio wave signal of a certain frequency. For the receiver that needs to receive this signal, it is a normal purpose signal, but for another receiver it is a non-purpose signal, that is, noise. The term interference is often used in electronics, and it is sometimes confused with the concept of noise. In fact, there is a difference. Noise is an electronic signal, and interference refers to an effect that is an adverse reaction to a circuit due to noise. While there is noise in the circuit, there is not necessarily interference. in digital circuits. It can often be observed with an oscilloscope that some small spikes mixed with the normal pulse signal are not expected, but a kind of noise. However, due to the relationship between circuit characteristics, these small spikes will not affect the logic of the digital circuit and cause confusion, so it can be considered that there is no interference.
When a noise voltage is large enough to disturb the circuit, the noise voltage is called interference voltage. And a circuit or a device, when it can maintain normal operation, the maximum noise voltage added is called the anti-interference tolerance or immunity of the circuit or device. Generally speaking, noise is difficult to eliminate, but you can try to reduce the intensity of the noise or improve the immunity of the circuit so that the noise will not form interference.
harmonic
Harmonic: It refers to the electricity whose frequency contained in the current is an integer multiple of the fundamental wave, generally refers to the electricity generated by Fourier series decomposition of the periodic non-sinusoidal electricity, and the rest of the current is greater than the fundamental frequency. In a broad sense, since the effective component of the AC power grid is a single frequency of the power frequency, any component different from the power frequency can be called a harmonic.
The reason for harmonic generation: Since the sinusoidal voltage is applied to the nonlinear load, when the current flows through the load, it does not have a linear relationship with the applied voltage, and the fundamental current is distorted to form a non-sinusoidal current, that is, there are harmonics in the circuit produce. The main nonlinear loads are UPS, switching power supply, rectifier, frequency converter, inverter, etc.
Compared with linear power supplies, switching power supplies (including AC/DC converters, DC/DC converters, AC/DC modules and DC/DC modules) have the most prominent advantage of high conversion efficiency, generally up to 80% to 85%. The highest can reach 90% to 97%. Secondly, the switching power supply uses a high-frequency transformer to replace the heavy power frequency transformer, which not only reduces the weight but also reduces the volume, so the application range is getting wider and wider. However, the disadvantage of switching power supply is that because its switching tube works in a high-frequency switching state, the output ripple and noise voltage are relatively large, generally about 1% of the output voltage (the lowest is about 0.5% of the output voltage), the best product The ripple and noise voltage of the linear power supply also have tens of mV; while the regulator tube of the linear power supply works in a linear state, there is no ripple voltage, and the output noise voltage is also small, and its unit is μV.
