NE555

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

6 of 8

www.unisonic.com.tw

QW-R106-001,F

TYPICAL APPLICATION NOTES

The application circuit shows astable mode configuration.

one

input of the upper comparator is at voltage of

2/3Vcc(R1=R2=R3),another input

is

connected to Pin 6.As soon

as

C1 is charging to higher than 2/3Vcc, transistor Q1

is turned ON and discharge C1 to collector

voltage of

transistor Q1. Therefore, the flip-flop circuit is reset and output is low. One input of lower comparator is at voltage of

1/3Vcc, discharge transistor Q1 turn off and C1 charges through RA and RB. Therefore, the flip-flop circuit is set

output high.

ln

Vcc

1

3

Vcc

Vcc

2

3

Vcc

0.693

−

−

⎛

⎝

⎜

⎜

⎜

⎞

⎠

⎟

⎟

⎟

=

Thus the total period time T is given by

Then the frequency of astable mode is given by

C1

*

)

R

(R

1.44

T

1

f

B

A

2

+

=

=

The duty cycle is given by

B

A

B

2R

R

R

T

T2

D.C.

+

=

=

.