The filter capacitor can reduce the AC impedance of the power supply. The reason is that the actual power supply always has internal resistance, and the transmission line also has impedance. The decoupling capacitor can allow a part of the instantaneously changed current to be directly exchanged on the capacitor. The DC/DC power supply circuit has the advantages of low power consumption and high power. The absorption filter has a capacitor and a capacitor circuit, which can completely eliminate the noise.
DC/DC circuit noise: Wenbo and noiseThe DC/DC power supply circuit has the advantages of low power consumption and high power, but at the same time, due to the conversion of the DC/DC circuit through the switching method, inevitable noise is introduced, specifically the ripple and noise of the power supply circuit.
In high-speed circuit design, high-end chips often have strict requirements on the ripple and noise of the power supply. Generally, the power supply ripple is controlled within 1% of the power supply voltage, and the noise should be limited to 3%-5% of the power supply voltage. within. For DC/DC power supplies, although the efficiency is higher than LDO, the ripple and noise are relatively large due to the reliance on the switching MOSFET.
Ripple and noise are fluctuations in the power supply.Ripple : The low-frequency component of the power supply fluctuation, generally less than 5MHz, is caused by the switching action of the MOSFET.
Noise : The high-frequency component of the power supply fluctuation is generally higher than 5MHz, and the composition is more complicated, generally including the switching noise of the MOSFET, white noise, and interference of surrounding signals.
For ripple and noise cancellation methods, there are common absorption and reflection filtering:
Absorption filtering : Absorption filtering consists of a capacitor and a capacitor circuit that completely eliminates noise.
Reflective filtering : consists of π, T or L or LC filter circuits. The principle is to pass the DC signal without attenuation through the filter circuit, while the higher frequency ripple and noise are returned to the source. The filter effect is achieved by using the impedance mismatch of the filter circuit. Its characteristic is that the filter circuit can not completely eliminate the noise, and the interference still exists in the circuit. According to the source impedance and the impedance of the load end, there are four reflective filter circuits to choose from. (a) and (c) are commonly used in DC/DC circuits.
Since the filtering principle of the LC filter circuit is reflection, interference still exists in the circuit. Therefore, in order to avoid the influence of these interferences on other circuits, other measures need to be taken:
Increase the filter capacitor. Both simple capacitors and magnetic beads have the effect of completely filtering out noise.
As shown in the figure above, in order to reduce the influence of the interference of the input power supply circuit on the power supply circuit, it is necessary to place a power supply filter circuit at A, the effect of which is to reflect the interference back to the 3.3V power plane, and to avoid reflection of these interferences to other For the effect of the 3.3V device, place several filter capacitors at B.
The magnetic beads are connected in series on the LC filter circuit, and the magnetic beads are used to absorb the power supply interference. As shown below
This not only exerts the reflection function of the LC filter circuit, but also fully utilizes the absorption function of the magnetic beads for interference such as ripple and noise.
Residential Elevators,Indoor Home Elevator,Capsule Lifts For Home,Small Elevators For Homes
XI'AN TYPICAL ELEVATOR CO., LTD , https://www.chinaxiantypical.com