TS555

9/12

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

the triggered mode, the charge and discharge

times and therefore frequency, are independent of

the supply voltage.

Figure 4:

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 :

The duty cycle is given by :

Figure 5:

Reset

Out

3

4

8

7

5

1

TS555

R

C

2

6

R

A

B

Control

Voltage

0.01 F

µ

f =

1

T

--- =

1.44

(

RA

2

RB

+

--------------------------------------

D =

RB

RA

2

RB

+

---------------------------

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