Application information

NE555 - SA555 - SE555

10/20

Doc ID 2182 Rev 6

Figure 15.

Typical schematics in astable operation

Figure 16 shows the 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:

T = t1 + t2 = 0.693 (R1 + 2R2) C1

The frequency of oscillation is then:

It can easily be found from Figure 17.

The duty cycle is given by:

Output

3

4

8

7

5

1

R1

C1

2

6

R2

Control

Voltage

NE555

V

0.01

f =

1

T

---

1.44

R1

2R2

+

()C1

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

=

t1

t1

t2

+

()

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

R1

R2

+

()

R1

2

R2

•

+

()

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

1

R2

R1

R2

+

()

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

–

==