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NE556D

Dual Timing Circuit

ON Semiconductor 

MC3456

Pulse Width Modulation

If the timer is triggered with a continuous pulse train in the

monostable mode of operation, the charge time of the

capacitor can be varied by changing the control voltage at

Pin 3. In this manner, the output pulse width can be

modulated by applying a modulating signal that controls the

threshold voltage.

Test Sequences

Several timers can be connected to drive each other for

sequential timing. An example is shown in Figure 24 where

the sequence is started by triggering the first timer which runs

for 10 ms. The output then switches low momentarily and

starts the second timer which runs for 50 ms and so forth.

Figure 22. Pulse Width Modulation Waveforms

Modulation Input Voltage 5.0 V/cm

Clock Input Voltage

5.0 V/cm

Output Voltage

5.0 V/cm

Capacitor Voltage

5.0 V/cm

t = 0.5 ms/cm

(RA = 10 kW, C = 0.02 mF, VCC = 15 V)

Figure 23. Pulse Width Modulation Circuit

+VCC (5.0 V to 15 V)

RL

Output

Clock

Input

4 (10)

Reset

VCC

Output

5 (9)

Trigger

1/2

MC3456

6 (8)

Gnd 7

14

Discharge

1 (13)

Threshold

2 (12)

Control

3 (11)

RA

C

Modulation

Input

Figure 24. Sequential Timing Circuit

VCC (5.0 V to 15 V)

9.1 k

Threshold

Discharge

1.0 µF

27 k

VCC

Reset

0.01 µF

1/2

MC3456

Trigger

Control

Output

0.001 µF

Gnd

9.1 k

Threshold

Discharge

Trigger

5.0 µF

27 k

VCC

Reset

0.01 µF

1/2

MC3456

Gnd

Control

Output

0.001 µF

50 k

Threshold

Discharge

Trigger

5.0 µF

VCC

Reset

0.01 µF

1/2

MC3456

Control

Output

Gnd

Load

Load

Load

8

MOTOROLA ANALOG IC DEVICE DATA

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