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Capacitance related ：
Capacitor filtering is used for load power supply （ Energy storage discharge ）, The load voltage will be more stable , Then the load works stably

When calculating the capacity of devices such as capacitors , Leave a margin , For example, the actual capacity of the capacitance can be calculated as 5 Times even 10 times , So the device won't “ Full load operation ”, The service life of the system can be greatly extended ;

When the load current <100mA or 500mA, Filter capacitors can be used 220uF or 330uF

For example, the actual voltage value of the capacitor can be taken as... Of the calculated value 1.5 Times even 2 times , For example, the typical value of capacitor voltage is 10V,16V,25V,35V.

Small capacitance ： Chip capacitors , Ceramic capacitor , Filter high frequency waves , Nonpolarity , A few pF- A few hundred nF;

High capacity capacitor ： Electrolytic capacitor , Low precision , Filter low frequency waves , Have polarity ; Large and small capacitors are also often used in combination .

Resistance dependent ：
Resistance selection ：

Current limiting action ： Generally, the resistance is large , And there will be a margin for limiting current , Accuracy is not high 5% have access to

Partial pressure action ： requirement 1% Resistance accuracy , Otherwise, the positive and negative deviation 5% It will lead to inaccurate partial pressure , Make a mistake

2.LED Working voltage ：3.3V, Working current 3.3-10mA, The greater the current led The brighter the light

3. Differential pressure when triode is on （ Pressure drop ）0.7V about , Calculate the circuit voltage , Every diode , Voltage drop 0.7V

4.AC AC voltage value ：220V,110V,24V,14V,16V

Half-wave rectifier ： The frequency is equal to the power frequency 50HZ, Full-wave rectifier ： The frequency is 2 Times the power frequency 100HZ

DC to DC （DC-DC）： Switch mode ： Efficient 70%, Complex structure and high cost ; Linear way ： The cost is low , Simple , Suitable for low power , High power has problems such as high heating and power consumption

LM7815 chip ： Linear depressurization mode , Certain voltage range input , Stable 15V Output

LM7805 chip ： Linear depressurization mode , Certain voltage range input , Stable 5V Output ; When the current flowing is 1A, Required power P<1W or 2W, Otherwise it will get hot , Need to add heat sink, etc . Pressure drop 10V Can be used within 1 individual 7805, When pressure drop >10V, Use 7815 Reuse 7805, Ensure no fever, serious etc , The power supply system is more stable and reliable . Flow current <500mA You can also use LM78L05.

Design process ： Achieve functionality —— Consider reliability —— Consider defects —— simplify —— Consider reliability , defects
push-pull circuit ： take 1 individual N Type a triode and P Type triode B Level and E Level corresponding connection , At the same time ,D1 and D2 It doesn't turn on at the same time . Classic drive circuit ： Improve I, Drive capability , Voltage follows , Current amplification .
Small power / Small current circuit ： triode ,Mos tube ; High Power / High current circuit ：Mos tube , as a result of Rce Far greater than Rds, However, when the current is large, the power consumption is very high .

Zhang Fei's three laws ：

Source , loop , impedance ;
The process of circuit design is waveform shaping ;
The essence of digital signal and analog signal research is slope ;
The first 17 Ministry ,18 Ministry ,19 Ministry

51 Single chip microcomputer ：Inter kernel ; 32 Single chip microcomputer ：ARM kernel ：ARM7/9/11,context arm12

ARM System examples ：

Contex A： function IOS System , For mobile phones , TV , The set-top box , Printers, etc

Contex B： Support real-time clock system , baseband , automobile , Industry , Medical treatment, etc.

Contex C：MCU, Various middle and low-end products

CPU Inside ：

Flash memory： Flash memory , Store in blocks , Cannot erase in bytes , Can only be erased in block form , Don't lose power

EEPROM： Store... In a single byte , Don't lose power

RAM： Power loss , Data can only be saved when power is on ; SRAM： Faster than RAM, Made of transistors ; DRAM： The speed is lower than RAM

DMA： Direct memory access , Reduce interruptions , Reduce data loss

Ethernet： Ethernet , It's a technical standard

PWM I/O mouth ADC DAC RTC： Real time clock , It is applied to high-precision clock requirements such as perpetual calendar

Synchronous serial communication ： The higher the baud rate , The faster the speed. , The transmission line is required to be short , Reduce the chance of error

asynchronous communication ： The clock is out of order , The deviation should not be too large , Otherwise, the data transmission will be wrong

UART： Asynchronous serial communication ： Large amount of data , Speed block , The characteristic is that the communication line is simple , Communication can be achieved with a simple cable , cost reduction , It is suitable for long distance communication , But applications with slow transmission speed .

SPI： Synchronous serial communication , Small amount of data , Slower ,SPI It's a high speed , full duplex , Synchronous communication bus , And only four wires are used on the chip pins , Saved the chip pins