74LS08 - 四倍的两个输入和门

2018年4月6日 - 0 Comments

74LS08 IC

74LS08 Pinout

74LS08 IC is a member of 74XXYY IC series. There are four AND gates in the chip and each gate have two inputs, hence the name QUADRUPLE 2- INPUT AND GATE. The gates in the chip are designed by SCHOTTKY TRANSISTORS for high speed logic operations.

74LS08 Pin configuration

74LS08 is a 14 PIN IC. The chip is available in different packages and is chosen depending on requirement. The description for each pin is given below.

Pin Number	Description
AND GATE 1
1	A1-INPUT1 of GATE 1
2	B1-INPUT2 of GATE 1
3	GATE1的Y1输出
AND GATE 2
4	A2-INPUT1 of GATE 2
5	门2的B2-Input2
6	Y2-OUTPUT of GATE2
AND GATE 3
9	A3-INPUT1 of GATE 3
10	B3-INPUT2门3
8	Y3-OUTPUT of GATE3
AND GATE 4
12	门4的A4输入1
13	B4-INPUT2 of GATE 4
11	门4的Y4输出
SHARED TERMINALS
7	gnd-连接到地面
14	VCC-Connected to positive voltage to provide power to all four gates

Features and Specifications

Operating voltage range: +4.75 to +5.25V
Recommended operating voltage: +5V
最大电源电压：7V
Maximum current allowed to draw through each gate output: 8mA
TTL outputs
低功耗
典型的上升时间：18NS
Typical Fall Time: 18ns
Operating temperature:0°C to 70°C
Storage Temperature: -65°C to 150°C

Note:Complete technical details can be found in the74LS08 Datasheetlinked at the bottom of this page.

74LS08 Equivalents

SN54LS08，IC 7408，HEF4081，任何两个晶体管都可以重新配置以形成A和门。

Where to Use 74LS08 IC

有很多应用IC 74LS08。下面提到的一些。

1. The chip is basically used where AND logic operation is needed. There are four AND gates in the chip, we can use one or all gates simultaneously.

2. The chip is used in systems where high speed AND operation is needed. As mentioned earlier the gates in the chip are designed by SCHOTTKY TRANSISTORS to make the switching delays of gates less. Because of this the chip can be used for high speed AND operations.

3. 74LS08 is one of cheapest IC present in market for AND logic operation. It is really popular and is available everywhere.

4.芯片提供某些系统中需要的TTL输出。

How to Use 74LS08 IC

The four AND gates in the chip mentioned earlier are connected internally as shown in diagram below.

74LS08内部结构

每个逻辑输入都在此处执行和操作。例如，Gate1在A1和B1之间执行和操作，并在Y1终端提供输出。

The truth table of AND gate is given as,

Input1	Input2	AND Output
LOW	LOW	LOW
高的	LOW	LOW
LOW	高的	LOW
高的	高的	高的

为了实现上述真相表，让我们简单和门申请电路as shown below.

使用74LS08的简单和门电路

For better understanding the internal working let us consider the simplified internal circuit of AND gate as shown below.

74LS08 Internal Circuit

In the circuit two transistors are connected in series to form a AND gate. The two inputs of AND gate are driven out from bases of the two transistors. These two inputs are connected to buttons to change the logic of inputs. Output of the AND gate is the voltage across resistor R1. This output is connected to a LED D1 trough a current limiting resistor R2. This LED is connected to detect the state of output.

The circuit working can be explained in few stages below:

stage1：当两个按钮不按下时。在这种状态下，两个晶体管的基碱基流的电流流为零。由于基部电流为Zeroboth晶体管Q1和Q2。因此，总电源电压VCC出现在晶体管Q1和Q2上。由于总VCC在跨晶体管中出现，因此跨电阻R1的下降将为零。因为输出不过是电阻R1的电压，所以它将很低。因此，当输入=低时，输出=低。

阶段2：按下任何一个按钮时。在此状态下，相对晶体管将离开另一个按钮。ON晶体管将充当短路和OFF晶体管的起作用，充当开路，其中总VCC出现在其上。因此，跨电阻R1的下降将为零。因为输出不过是电阻R1的电压，所以它将很低。因此，当一个输入=低时，输出=低。

Stage3:When both buttons are pressed. Both transistors will be ON and voltage across both of them will be zero.At this time the total VCC appears across resistor R1.Because output is nothing but voltage across resistor R1 it will be HIGH. So when both INPUT = HIGH, OUTPUT = HIGH.

验证这三个状态后，您可以说我们满足了上述真相表。我们还可以通过真实表编写逻辑方程式和门，y = a.b或a+b

Like this we can use each gate of the chip depending on requirement.