ASTABLE OPERATION

When the circuit is connected as shown in figure 4

(pin 2 and 6 connected) it triggers itself and free

runs as a multivibrator. The external capacitor

cisely set by the ratio of these two resistors.

In the astable mode of operation, C charges and

triggered mode, the charge and discharge times

and therefore frequency, are independent of the

supply voltage.

Figure 5 shows actual waveforms generated in 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 of oscillation is then :

f

= 1

T

=

1.44

The duty cycle is given by : D

=

Reset

Out

3

4

8

7

5

1

TS555

R

C

2

6

R

A

B

Control

Voltage

0.01 F

µ

Figure 4

Ω

Ω

µ

t = 0.5 ms / div

OUTPUT VOLTAGE = 5.0V/div

CAPACITOR VOLTAGE = 1.0V/div

L

R = R = 4.8 k , C = 0.1 F , R = 1.0k

AB

Figure 5

TS555C,I,M

9/12