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MC1455 Folha de dados(PDF) 6 Page - ON Semiconductor |
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MC1455 Folha de dados(HTML) 6 Page - ON Semiconductor |
6 / 10 page MC1455, MC1455B, NCV1455B http://onsemi.com 6 Figure 15. Monostable Waveforms Figure 16. Time Delay Figure 17. Astable Circuit Figure 18. Astable Waveforms (RA = 10 kW, C = 0.01 mF, RL = 1.0 kW, VCC = 15 V) (RA = 5.1 kW, C = 0.01 mF, RL = 1.0 kW; RB = 3.9 kW, VCC = 15 V) t = 20 ms/cm t = 50 ms/cm 100 10 1.0 0.1 0.01 0.001 10 ms 100 ms 1.0 ms 10 ms 100 ms 1.0 10 100 td, TIME DELAY (s) RL +VCC (5.0 V to 15 V) Reset VCC 8 7Discharge 6Threshold 5 Control Voltage 1 2 Trigger Output 3 4 RA RL MC1455 C RB Astable Mode In the astable mode the timer is connected so that it will retrigger itself and cause the capacitor voltage to oscillate between 1/3 VCC and 2/3 VCC. See Figure 17. The external capacitor changes to 2/3 VCC through RA and RB and discharges to 1/3 VCC through RB. By varying the ratio of these resistors the duty cycle can be varied. The charge and discharge times are independent of the supply voltage. The charge time (output high) is given by: t1 + 0.695(RA ) RB)C The discharge time (output low) is given by: t2 + 0.695(RB)C Thus the total period is given by: T + t1 ) t2 + 0.695(RA ) 2RB)C The frequency of oscillation is then: f + 1 1 + 1.44 (RA ) 2RB)C and may be easily found as shown in Figure 19. The duty cycle is given by: DC + RB RA ) 2RB To obtain the maximum duty cycle RA must be as small as possible; but it must also be large enough to limit the discharge current (Pin 7 current) within the maximum rating of the discharge transistor (200 mA). The minimum value of RA is given by: RA w VCC(Vdc) I7 (A) w VCC(Vdc) 0.2 Figure 19. Free Running Frequency 100 10 1.0 0.1 0.01 0.001 (RA + 2 RB) 0.1 1.0 10 100 1.0 k 10 k 100 f, FREE RUNNING FREQUENCY (Hz) |
Nº de peça semelhante - MC1455 |
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Descrição semelhante - MC1455 |
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