NE555 데이터 시트보기 (PDF) - STMicroelectronics

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NE555

General-purpose single bipolar timers

STMicroelectronics 

Application information

Figure 15. Typical schematics in astable operation

VCC = 5 to 15V

NE555 - SA555 - SE555

R1

4

8

Output

3

7

NE555

R2

Control

Voltage

5

0.01μF

1

6

2

C1

Figure 16 shows the actual waveforms generated in this mode of operation.

The charge time (output HIGH) is given by:

t1 = 0.693 (R1 + R2) C1

and the discharge time (output LOW) by:

t2 = 0.693 (R2) C1

Thus the total period T is given by:

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

The frequency of oscillation is then:

f

=

-1--

T

=

--------------1----.-4----4---------------

(R1 + 2R2)C1

It can easily be found from Figure 17.

The duty cycle is given by:

---------t--1---------- = -----(--R-----1-----+-----R-----2---)-----

(t1 + t2) (R1 + 2 • R2)

= 1–

(---R-----1--R--+---2--R-----2----)

10/20

Doc ID 2182 Rev 6

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