t = 0.5 ms / div

OUTPUT VOLTAGE = 5.0V/div

CAPACITOR VOLTAGE = 1.0V/div

R1 = R2 = 4.8k

L

Figure 14

C

(

µF)

10

1.0

0.1

0.01

0.001

0.1

1

10

100

1k

10k

f (Hz)

o

R

1

+

R2

=

10

10

10

k

Ω

Figure 14 shows actual waveforms generatedin this

mode of operation.

The charge time (output HIGH) is given by :

and the discharge time (output LOW) by :

Thus the total period T is given by :

The frequency ofoscillation is them :

f

=

1

T

=

1.44

and may be easily found by figure 15.

The duty cycle is given by :

D

=

Output

3

48

7

5

1

R1

C1

2

6

R2

Control

Voltage

NE555

V

0.01

µF

Figure 13

PULSE WIDTH MODULATOR

When the timer is connected in the monostable

mode and triggered with a continuous pulse train,

the output pulse width can be modulated by a signal

applied to pin 5. Figure 16 shows the circuit.

Trigger

Output

R

C

NE555

2

4

3

1

5

6

7

Modulation

Input

8

A

Figure 16 : Pulse Width Modulator.

NE555/SA555/SE555

7/10