Practical circuit analysis 3

It's on it 12v The power supply , Here is gnd, Here is the general 12v After DC adjustment , It is provided to the backlight through two interfaces , The backlight can be directly connected to the two interfaces to emit light .

d6 Is a protection 2 diode , It can ensure that the front and rear circuits are isolated

r36 yes 0 Ohmic resistance , That is, short circuit state , The resistance here is replaced by the resistance of other resistance values , It can adjust the current in the circuit .

cd3 It is a diode with polarity , It can filter and protect the circuit

c31 It is a capacitor connected between the positive and negative poles of the DC power supply , This is a common structure , Play a filtering role 、 Isolation 、 The role of protection , When using DC power supply, a capacitor is indirectly connected at the output positive and negative poles according to the principle that the voltage at both ends of the capacitor cannot change suddenly , In order to stabilize the voltage , It is called filtering in electronic devices .

 Filtration exhaustion （ It is a large capacity, usually by electrolysis ）、 Decoupling 、 High frequency bypass （ Generally small and medium capacity ）

r37 It mainly plays the role of current limiting protection .

r38c32 ditto

Connect a capacitor between the DC power supply and the ground , What is its role ？ - 21ic Electronic network

We all know that a capacitor is connected between the DC power supply and the ground , So what is its function ?

1, In DC power supply (Vcc) Capacitance connected in parallel with the ground can be called filter capacitance . The filter capacitor filters out the clutter and AC components of the power supply , Smooth pulsating DC voltage , Store electrical energy . General value 100-4700uF. The value is related to the load current and the purity of the power supply , The larger the capacity, the better . Sometimes there is a capacitor with smaller capacity next to a large capacitor , It's called high frequency decoupling capacitor . It is also a type of filtering, which is used to filter the high-frequency clutter in the power supply to avoid self excitation of the circuit , Stabilize the working state of the circuit . General value 0.1-10uF. The value is related to the frequency of filtering clutter .

The function of this connection is generally called “ Decoupling ”, Also called “ Decoupled connection ”、“ bypass ” capacitance , Often arranged in the power supply 、IC And functional module circuits . With insensible porcelain pieces 、 Single stone capacitance is better .

The function is to provide a path for high-frequency signals , Reduce the internal resistance of the power supply , Remove the power and ground wires from the copper clad plate “ Take a long line ” Influence , Prevent between the circuits of various parts of the public power supply “ Harmful interactions ” wait . Commonly used 10nF.

2, On the development board , Usually, there are many... Between DC power supply and ground 0.1uF Non electrolytic capacitors and 10uF Electrolytic capacitor .

These capacitors , The purpose is to make the low impedance between the power line and the ground wire , The power supply is close to the ideal voltage source . You can say it's filtering , But we need to find out what wave is filtering . Not the ripple of the power filter , But the ripple caused by the current change of a chip on the power line , So that it does not affect other chips .

Use 0.1uF Non polar capacitance and 10uF Electrolytic capacitors are connected in parallel , Because the parasitic inductance of electrolytic capacitor is relatively large , Poor ability to eliminate high-frequency ripple . The nonpolar capacitance has small parasitic inductance , Good ability to filter out high-frequency ripple .. However, if the capacity is selected according to the requirements of low frequency , Then the volume of nonpolar capacitor is too large , The cost is also high. , Electrolytic capacitors are small in size , Similarly, the price of capacity is cheaper . Therefore, two capacitors are connected in parallel .

You design the circuit yourself , It should also be used in this way , Moreover, the position and wiring of each capacitor are very particular .

Can only say two principles ：

1)、 The connecting lines from both ends of each small capacity non-polar capacitor to the power pin and ground pin of the chip shall be as short as possible , The shorter the better .

2)、 The power supply is usually introduced by other circuit boards , Electrolytic capacitors usually have only one or two on each circuit board . An electrolytic capacitor , Put it where the power supply enters the circuit board . At this time, of course, the electrolytic capacitor is far away from each chip , However, electrolytic capacitors mainly work at lower frequencies , So it doesn't matter to be a little further . If two electrolytic capacitors are used on the circuit board , The other one is near the chip that consumes the most power .

These and circuit board component layout 、 Routing arrangement of ground wire ( Multilayer boards usually have layers ) Have a relationship