MC1455 データシートの表示（PDF） - ON Semiconductor

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MC1455

Timers

ON Semiconductor 

MC1455, MC1455B, NCV1455B

100

10

1.0

0.1

0.01

t = 50 ms/cm

(RA = 10 kW, C = 0.01 mF, RL = 1.0 kW, VCC = 15 V)

Figure 15. Monostable Waveforms

+VCC (5.0 V to 15 V)

0.001

10 ms 100 ms 1.0 ms 10 ms 100 ms 1.0

10

100

td, TIME DELAY (s)

Figure 16. Time Delay

Reset

RL

4

Output

VCC

RA

8

7 Discharge

3

Trigger

MC1455

6 Threshold

RB

5

RL

2

1

Control

Voltage

C

Figure 17. Astable Circuit

t = 20 ms/cm

(RA = 5.1 kW, C = 0.01 mF, RL = 1.0 kW; RB = 3.9 kW, VCC = 15 V)

Figure 18. Astable Waveforms

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

+

(RA

1.44

) 2RB)C

and may be easily found as shown in Figure 19.

The duty cycle is given by:

DC

+

RA

RB

) 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

100

10

1.0

0.1

0.01

(RA + 2 RB)

0.001

0.1

1.0

10

100 1.0 k

10 k 100

f, FREE RUNNING FREQUENCY (Hz)

Figure 19. Free Running Frequency

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