NE555 查看數據表（PDF） - Unisonic Technologies

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NE555

SINGLE TIMER

Unisonic Technologies 

NE555

LINEAR INTEGRATED CIRCUIT

„ TYPICAL APPLICATION NOTES

The application circuit shows astable mode configuration.

Pin 6 (Threshold ) is tied to Pin 2 ( Trigger ) and Pin 4 ( reset ) is tied to VCC ( Pin 8 ). The external capacitor C1 of

Pin 6 and Pin 2 charges through RA, RB and dischages through RB only. In the internal circuit of UTC NE555 , 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.

That is, when C1 charges through RA and RB , output is high and when C1 discharge through RB ,output is low.

The charge time(output is high) t1 is 0.693(RA+RB) C1 and the discharge time (output is low) T2 is 0.693 RB*C1.

⎛

⎜

ln⎜

⎜

⎝

Vcc−

Vcc−

1 Vcc

3

2 Vcc

3

⎞

⎟

⎟

⎟

⎠

= 0.693

T1=0.693*(RA+RB)*C1

Thus the total period time T is given by

T2=0.693*RB*C1

T=T1+T2=0.693(RA+2RB)*C1.

Then the frequency of astable mode is given by

1

1.44

f= =

T (RA + 2RB) * C1

The duty cycle is given by

T2

RB

D.C. = =

T RA + 2RB .

UNISONIC TECHNOLOGIES CO., LTD

www.unisonic.com.tw

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QW-R106-001,F

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