전자부품 데이터시트 검색엔진 |
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NE555 데이터시트(PDF) 5 Page - Fairchild Semiconductor |
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NE555 데이터시트(HTML) 5 Page - Fairchild Semiconductor |
5 / 14 page LM555/NE555/SA555 5 5 5 5 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, VC1 increases exponentially with the time constant t=RA*C and reaches 2Vcc/3 at td=1.1RA*C. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RAC, the longer it takes for the VC1 to reach 2Vcc/3. In other words, the time constant RAC controls the output pulse width. 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 RA and C. Figure 3 shows the general waveforms during the monostable operation. 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. 2. Astable Operation 2. Astable Operation 2. Astable Operation 2. Astable Operation Figure 4. Waveforms of Monostable Operation (abnormal) Figure 4. Waveforms of Monostable Operation (abnormal) Figure 4. Waveforms of Monostable Operation (abnormal) Figure 4. Waveforms of Monostable Operation (abnormal) 100m 100m 100m 100m 1 11 110 10 10 10 100 100 100 100 1k 1k 1k 1k 10k 10k 10k 10k 100k 100k 100k 100k 1E-3 1E-3 1E-3 1E-3 0.01 0.01 0.01 0.01 0.1 0.1 0.1 0.1 1 11 1 10 10 10 10 100 100 100 100 (R (R (R (R A A A A +2R +2R +2R +2R B B B B) ))) Fr equency(Hz) Fr equency(Hz) Fr equency(Hz) Fr equency(Hz) Figure 5. Astable Circuit Figure 5. Astable Circuit Figure 5. Astable Circuit Figure 5. Astable Circuit Figure 6. Capacitance and Resistance vs. Frequency Figure 6. Capacitance and Resistance vs. Frequency Figure 6. Capacitance and Resistance vs. Frequency Figure 6. Capacitance and Resistance vs. Frequency 1 5 6 7 8 4 2 3 RESET Vcc DISCH THRES CONT GND OUT TRIG +Vcc RA C1 C2 RL RB |
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