công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
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LM555 bảng dữ liệu(PDF) 7 Page - National Semiconductor (TI) |
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LM555 bảng dữ liệu(HTML) 7 Page - National Semiconductor (TI) |
7 / 12 page Applications Information MONOSTABLE OPERATION In this mode of operation, the timer functions as a one-shot (Figure 1). The external capacitor is initially held discharged by a transistor inside the timer. Upon application of a nega- tive trigger pulse of less than 1/3 V CC to pin 2, the flip-flop is set which both releases the short circuit across the capacitor and drives the output high. The voltage across the capacitor then increases exponen- tially for a period of t = 1.1 R A C, at the end of which time the voltage equals 2/3 V CC. The comparator then resets the flip-flop which in turn discharges the capacitor and drives the output to its low state. Figure 2 shows the waveforms gen- erated in this mode of operation. Since the charge and the threshold level of the comparator are both directly propor- tional to supply voltage, the timing interval is independent of supply. During the timing cycle when the output is high, the further application of a trigger pulse will not effect the circuit so long as the trigger input is returned high at least 10µs before the end of the timing interval. However the circuit can be reset during this time by the application of a negative pulse to the reset terminal (pin 4). The output will then remain in the low state until a trigger pulse is again applied. When the reset function is not in use, it is recommended that it be connected to V CC to avoid any possibility of false triggering. Figure 3 is a nomograph for easy determination of R, C values for various time delays. NOTE: In monostable operation, the trigger should be driven high before the end of timing cycle. ASTABLE OPERATION If the circuit is connected as shown in Figure 4 (pins 2 and 6 connected) it will trigger itself and free run as a multivibrator. The external capacitor charges through R A +RB and dis- charges through R B. Thus the duty cycle may be precisely set by the ratio of these two resistors. In this mode of operation, the capacitor charges and dis- charges between 1/3 V CC and 2/3 VCC. As in the triggered mode, the charge and discharge times, and therefore the frequency are independent of the supply voltage. 00785105 FIGURE 1. Monostable 00785106 VCC = 5V Top Trace: Input 5V/Div. TIME = 0.1 ms/DIV. Middle Trace: Output 5V/Div. RA = 9.1kΩ Bottom Trace: Capacitor Voltage 2V/Div. C = 0.01µF FIGURE 2. Monostable Waveforms 00785107 FIGURE 3. Time Delay 00785108 FIGURE 4. Astable www.national.com 7 |
Số phần tương tự - LM555 |
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Mô tả tương tự - LM555 |
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