[note] common combined filter circuit

Learning video

What is? T Type filtering ？ And L type 、π Type filter comparison , It's easy to understand
Video author ： Electronic electrician Huang Chao thought
I highly recommend you to watch his video ！！！

Common filter circuit

capacitance 、 inductance 、 Introduction to resistance

Need to understand these circuits , First of all, we have to check the inductance 、 capacitance 、 There is some basic understanding of resistance ：

resistance ： It has the characteristic of blocking current from passing through the circuit , A resistor is a device that blocks the flow of current in a circuit , The essence of current is that electrons flow in objects , When the attraction of atoms and electrons in the object is relatively strong , The greater the resistance of this object , The smaller the vice . The resistance of the wire is very small , The resistance of the insulator is very high , Close to open circuit . When current flows through a resistive device , There will be a voltage difference between the two ends of the resistance , Also called voltage drop , The energy lost is converted into the heat of the resistance , The electric water heater uses this principle . Take advantage of this feature , Resistance is often used in a circuit to generate partial voltage 、 Set magnification 、 Static working point, etc .

capacitance ： A container for storing electric charges in a circuit , It can be imagined as two panels storing charges at a distance , When a positive charge is constantly pouring into one of the panels , The other panel will continue to attract negative charges , In order to make the whole capacitor reach the electric neutral state . Capacitance is divided into non-polar capacitance and polar capacitance , The two panels of the nonpolar capacitor can store both positive and negative charges ; The positive pole with polar capacitance can only store positive charge , The negative pole can only store negative charges , Otherwise, the capacitor will be punctured . In the circuit , This storage charge characteristic of capacitance is mainly used for filtering . Capacitance has two main characteristics in the circuit , A resistance characteristic , The other is the phase shift characteristic , These two characteristics are related to the frequency of the signal . For resistance characteristics , The lower the frequency , The greater the resistance of the capacitor , The smaller the vice . For capacitance , There are several key points to remember in circuit analysis , That's it Every other day 、 Turn on high frequency resistance and low frequency resistance 、 The voltage at both ends shall not change suddenly .

capacitance ： A container for storing electric charges in a circuit , It can be imagined as two panels storing charges at a distance , When a positive charge is constantly pouring into one of the panels , The other panel will continue to attract negative charges , In order to make the whole capacitor reach the electric neutral state . Capacitance is divided into non-polar capacitance and polar capacitance , The two panels of the nonpolar capacitor can store both positive and negative charges ; The positive pole with polar capacitance can only store positive charge , The negative pole can only store negative charges , Otherwise, the capacitor will be punctured . In the circuit , This storage charge characteristic of capacitance is mainly used for filtering . Capacitance has two main characteristics in the circuit , A resistance characteristic , The other is the phase shift characteristic , These two characteristics are related to the frequency of the signal . For resistance characteristics , The lower the frequency , The greater the resistance of the capacitor , The smaller the vice . For capacitance , There are several key points to remember in circuit analysis , That's straight through 、 Turn on high frequency resistance and low frequency resistance 、 The voltage at both ends shall not change suddenly .

Simply speaking ：
Resistance can prevent current from passing , It can start and divide the voltage in the circuit 、 step-down 、 Current limiting 、 load 、 shunt 、 Zoning and other functions ;
The function of capacitance is to filter in the circuit 、 coupling 、 bypass 、 Tuning and energy conversion ;
The main function of inductance is to have direct current in the circuit 、 AC resistance , Pass low frequency 、 The effect of blocking high frequency .

What is low pass filtering and high pass filtering ？

Low pass filtering and high pass filtering use the characteristics of capacitor on high frequency and resistance on low frequency to filter .

The capacitor of this circuit discharges to ground , When the frequency of the input signal is low , The capacitor will filter out this signal , At this time, the capacitor discharges to the ground , The output waveform is stable .

The capacitance of this circuit discharges to the output , When the frequency of the input signal is low , The capacitance will prevent the signal from passing , Only when the signal frequency is high , This capacitor discharges to the output , The output end is a high-frequency signal .
If you can't understand , It is recommended to watch this video

LC Filtering and RC wave filtering

LC Filtering is to use the characteristics of inductance and capacitance to filter ,RC Filtering is to use the characteristics of resistance and capacitance to filter .

above RC circuit , Capacitance has high impedance to low-frequency signal , It can absorb low-frequency signals , So the output is capacitance filtered .
Below LC circuit , Using the characteristics of inductance and low frequency resistance and high frequency , Then it is filtered by capacitance , It is a double filter circuit .

above RC circuit , It makes use of the characteristics of the same high frequency resistance and low frequency , Low frequency signals will be filtered out by capacitors , Only when it reaches its barrier, the corresponding high-frequency signal can pass through the capacitor .
Below LC circuit , It makes use of the characteristics of the same high frequency resistance and low frequency , Low frequency signals will be filtered out by capacitors , The only difference is that the low-frequency part coming through the inductor will be filtered out to the ground , It achieves the effect of double filtering low frequency .

Other T type Π Type is the same , See video analysis for details . relatively speaking ,Π Type a filter will have a better effect .