NE555 데이터 시트보기 (PDF) - STMicroelectronics

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NE555

General-purpose single bipolar timers

STMicroelectronics 

NE555 - SA555 - SE555

Application information

Figure 20 shows the waveforms generator by the linear ramp.

The time interval is given by:

T = --R(--2---1-/-3---V--V--c--c-c--c------R-V---E-B----E-(--R---(-1-R---+-1--R-+---2-R---)-2--C-)-- VBE = 0.6V

Figure 20. Linear ramp

VCC = 5 V

Time:

20 µs/DIV

R1 + 47 kΩ

R2 = 100 kΩ

RE = 2.7 kΩ

C = 0.01 µF

Top trace: input 3 V/DIV

Middle trace: output 5 V/DIV

Bottom trace: output 5 V/DIV

Bottom trace: capacitor voltage 1 V/DIV

4.5

50% duty cycle oscillator

For a 50% duty cycle, the resistors RA and RB can be connected as in Figure 21. The time

period for the output high is the same as for astable operation (see Section 4.2 on page 9):

t1 = 0.693 RA C

For the output low it is

t2= [(R. RB)/(RA+RB)].C.Ln

R-----B------–----2----R-----A--

2RB – RA

Thus the frequency of oscillation is:

f = -------1---------

t1 + t2

Doc ID 2182 Rev 6

13/20

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