欢迎访问ic37.com |
会员登录 免费注册
发布采购

LM555 参数 Datasheet PDF下载

LM555图片预览
型号: LM555
PDF下载: 下载PDF文件 查看货源
内容描述: 单TIMER [Single Timer]
分类和应用:
文件页数/大小: 14 页 / 152 K
品牌: FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
 浏览型号LM555的Datasheet PDF文件第1页浏览型号LM555的Datasheet PDF文件第2页浏览型号LM555的Datasheet PDF文件第3页浏览型号LM555的Datasheet PDF文件第4页浏览型号LM555的Datasheet PDF文件第6页浏览型号LM555的Datasheet PDF文件第7页浏览型号LM555的Datasheet PDF文件第8页浏览型号LM555的Datasheet PDF文件第9页  
LM555/NE555/SA555  
Figure 1 illustrates a monostable circuit. In this mode, the timer generates a fixed pulse whenever the trigger voltage falls  
below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's  
internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor C1  
and setting the flip-flop output at the same time.  
The voltage across the external capacitor C1, V increases exponentially with the time constant t=R *C and reaches 2Vcc/3  
C1  
A
at td=1.1R *C. Hence, capacitor C1 is charged through resistor R . The greater the time constant R C, the longer it takes  
A
A
A
for the V to reach 2Vcc/3. In other words, the time constant R C controls the output pulse width.  
C1  
A
When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop,  
turning the discharging Tr. on. At this time, C1 begins to discharge and the timer output converts to low.  
In this way, the timer operating in the monostable repeats the above process. Figure 2 shows the time constant relationship  
based on R and C. Figure 3 shows the general waveforms during the monostable operation.  
A
It must be noted that, for a normal operation, the trigger pulse voltage needs to maintain a minimum of Vcc/3 before the timer  
output turns low. That is, although the output remains unaffected even if a different trigger pulse is applied while the output is  
high, it may be affected and the waveform does not operate properly if the trigger pulse voltage at the end of the output pulse  
remains at below Vcc/3. Figure 4 shows such a timer output abnormality.  
Figure 4. Waveforms of Monostable Operation (abnormal)  
2. Astable Operation  
+Vcc  
100  
(RA+2RB)  
R
A
10  
1
4
8
RESET  
Vcc  
7
6
DISCH  
TRIG  
OUT  
2
3
R
B
0.1  
THRES  
CONT  
0.01  
C1  
5
GND  
1E-3  
100m  
R
C2  
L
1
1
10  
100  
1k  
10k  
100k  
Frequency(Hz)  
Figure 6. Capacitance and Resistance vs. Frequency  
Figure 5. Astable Circuit  
5