Discrete device ~ resistance capacitance

1、 Commonly used resistance types

 1> Carbon film resistance ：

Color ring resistance reading ： Brown red, orange yellow and green , Blue purple gray white black , golden ：5%, silvery ：10%.

give an example ： Brown red red gold

The resistance value is 12×10^2=1.2kΩ Error is ±5%

2> Metal film resistance

The appearance is very similar to that of the carbon film resistor , You can directly scrape the paint on the surface with a knife , The carbon film is black , The metal film is white . Temperature stability of metal film resistance , The accuracy is much better than that of carbon film resistance .

3> Chip resistance

The chip resistor consists of ： Ceramic substrate 、 A slurry with a certain resistivity , resist film , electrode .

Common sizes are as follows ：

Electrical parameters

Power of chip resistor ：

0402 1/16W

0603 1/10W

0805 1/8W

1206 1/4W

Two 、 capacitance

1、 Common capacitor types

1> Electrolytic capacitor

The structure diagram of the inner core is as follows , There is also an aluminum shell outside .

The physical disassembly is as follows ：

The parameters of electrolytic capacitor are as follows ：

In the picture Ripple Current( Ripple current ) This is also a very important parameter , We need to pay attention to ：

One of the key functions of any capacitor is to eliminate ripple current , That is, the AC current flowing through the capacitor RMS value . Excessive internal heating caused by higher than rated ripple current , So as to shorten the service life of the capacitor . In extreme cases , Internal high temperature will cause the relief valve to work , And destroy the equipment . in general , The electrolytic capacitor must be used within the allowable ripple current range .

Of electrolytic capacitors ESR

The tangent of loss angle is the ratio of active power to reactive power , At low frequencies , such as 120Hz, Inductive reactance can be ignored , Therefore, the loss angle formula can be obtained ：

Ordinary aluminum electrolytic capacitors cannot be found in the specification ESR Value , But there is a loss angle loss angle parameter , We can calculate , But this kind of calculation can only be made in 120HZ The situation of , Because at high frequencies ,ESL Can't ignore , The formula is not applicable .

  Of electrolytic capacitors ESR It changes with the increase of frequency , As shown in the figure below ：

2> Solid state capacitor

Solid state capacitor is also a kind of electrolytic capacitor , Just replace the electrolyte of aluminum electrolytic capacitor with conductive polymer material , Conductive polymer materials usually have higher conductivity than electrolyte 2～3 An order of magnitude , Applied to aluminum electrolytic capacitors can greatly reduce ESR、 Improve temperature frequency characteristics .

The parameters are as follows , It can be seen that there are several ripple currents A,ESR Only a few dozen mΩ.

Judging from the appearance of solid aluminum electrolytic capacitor or ordinary aluminum electrolytic capacitor, you can see whether there is an explosion-proof tank on the top , Some of them are ordinary aluminum electrolytic capacitors .

3> Chip capacitors

The main materials of chip capacitors are X5R,X7R,C0G(NP0), Temperature stability of three materials ,C0G It has the best temperature stability ,X7R second ,X5R The worst ,X5R The advantage of SMD capacitor is its high capacitance .

Chip capacitor ESL

High speed circuit design , There is a problem with ground bombs , When we reduce the ground bounce , The most direct way is to reduce the impedance of the return path , We want to switch from the power layer to the stratum , At high frequency, capacitance is equivalent to short circuit , Is the reference layer the same as the power layer and the stratum , Is it possible to solve the problem of ground bombs by adding more capacitors ？

It's no use adding capacitance ：

We can know from the impedance curve of the capacitance in the figure below , At higher frequencies ESL Played a major role , The impedance of the capacitor is relatively large .

4> Other types of capacitors

Other commonly used capacitors are polypropylene CBB capacitance , Film capacitance , Tantalum capacitors, etc

CBB The temperature stability of the capacitor is also good , The capacity value can be larger , So in C0G When a large capacitance cannot be found , Think about CBB.

2、 Calculation of decoupling capacitance

example ： In the figure C1 Decoupling capacitor ,LED1 For load ,R1 Equivalent to internal resistance . If the load is required to be 10us Domestic supply 1A electric current , The load voltage is 2V, Allowable voltage fluctuation 5%, So the energy change in the capacitance is Q = C * V = C * ( 2 * 5%), Because the capacitance is still in 10us Provide 1A electric current , So there is Q = I * T = 1A * 10us, therefore C = I * dt / dv = 10 / 0.1 = 100uF.