Datasheet NE555, SA555, NA555 (Diodes) - 7
| 制造商 | Diodes |
| 描述 | Precision Timers |
| 页数 / 页 | 14 / 7 — NE555/SA555/NA555. PRECISION TIMERS. Typical Applications … |
| 文件格式/大小 | PDF / 742 Kb |
| 文件语言 | 英语 |
NE555/SA555/NA555. PRECISION TIMERS. Typical Applications Characteristics. Monostable Operation. NEW PROD
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NE555/SA555/NA555 PRECISION TIMERS Typical Applications Characteristics Monostable Operation
For monostable operation, any of the ‘555 timers can be connected as shown in Figure 1. If the output is low, application of a negative-going pulse to the trigger (TRIG) sets the internal flip-flop and drives the output high. Capacitor C is then charged through RA until the voltage across the capacitor reaches the threshold voltage of the threshold (THRES) input. If TRIG has returned to a high level, the output of the threshold comparator resets the internal flip-flop, drives the output low, and discharges C.
VCC
T
(5V to 15V)
UC
RA R 5 L 8
CONT V 4 CC
RESET
7 DISCH 3
OUT Output
NEW PROD
6 THRES
2 Input TRIG
C GND
1
Fig 1. Monostable operation
Monostable operation is initiated when TRIG voltage falls below the trigger threshold. Once initiated, the sequence ends only if TRIG is high for at least 10μs before the end of the timing interval. When the trigger is grounded, the comparator storage time can be as long as 10μs, which limits the minimum monostable pulse width to 10μs. Because of the threshold level and saturation voltage of Q1, the output pulse duration is approximately tW = 1.1RAC. Figure 3 is a plot of the time constant for various values of RA and C. The threshold levels and charge rates both are directly proportional to the supply voltage, VCC. The timing interval is, therefore, independent of the supply voltage, so long as the supply voltage is constant during the time interval. Applying a negative-going trigger pulse simultaneously to RESET and TRIG during the timing interval discharges C and reinitiates the cycle, commencing on the positive edge of the reset pulse. The output is held low as long as the reset pulse is low. To prevent false triggering, when RESET is not used, it should be connected to VCC.
Fig. 2 Typical Monostable Waveforms Fig. 3 Output Pulse Duration vs. Capacitance
NE555/SA555/NA555 7 of 14 February 2012 Document number: DS35112 Rev. 4 - 2
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© Diodes Incorporated
For monostable operation, any of the ‘555 timers can be connected as shown in Figure 1. If the output is low, application of a negative-going pulse to the trigger (TRIG) sets the internal flip-flop and drives the output high. Capacitor C is then charged through RA until the voltage across the capacitor reaches the threshold voltage of the threshold (THRES) input. If TRIG has returned to a high level, the output of the threshold comparator resets the internal flip-flop, drives the output low, and discharges C.
VCC
T
(5V to 15V)
UC
RA R 5 L 8
CONT V 4 CC
RESET
7 DISCH 3
OUT Output
NEW PROD
6 THRES
2 Input TRIG
C GND
1
Fig 1. Monostable operation
Monostable operation is initiated when TRIG voltage falls below the trigger threshold. Once initiated, the sequence ends only if TRIG is high for at least 10μs before the end of the timing interval. When the trigger is grounded, the comparator storage time can be as long as 10μs, which limits the minimum monostable pulse width to 10μs. Because of the threshold level and saturation voltage of Q1, the output pulse duration is approximately tW = 1.1RAC. Figure 3 is a plot of the time constant for various values of RA and C. The threshold levels and charge rates both are directly proportional to the supply voltage, VCC. The timing interval is, therefore, independent of the supply voltage, so long as the supply voltage is constant during the time interval. Applying a negative-going trigger pulse simultaneously to RESET and TRIG during the timing interval discharges C and reinitiates the cycle, commencing on the positive edge of the reset pulse. The output is held low as long as the reset pulse is low. To prevent false triggering, when RESET is not used, it should be connected to VCC.
Fig. 2 Typical Monostable Waveforms Fig. 3 Output Pulse Duration vs. Capacitance
NE555/SA555/NA555 7 of 14 February 2012 Document number: DS35112 Rev. 4 - 2
www.diodes.com
© Diodes Incorporated