Application information

NE555 - SA555 - SE555

14/20

Figure 20 shows the waveforms generator by the linear ramp.

The time interval is given by:

Figure 20.

Linear ramp

4.5

50% duty cycle oscillator

period for the output high is the same as for astable operation (see Section 4.2 on page 10):

For the output low it is

Thus the frequency of oscillation is:

T =

(2/3 Vcc RE (R1+R2) C

R1 Vcc - VBE (R1+R2)

---------------------------------------------------------------- VBE = 0.6V

Time:

20µs/DIV

C = 0.01µF

Top trace: input 3V/DIV

Middle trace: output 5V/DIV

Bottom trace: output 5V/DIV

Bottom trace: capacitor voltage 1V/DIV

t

2

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

RB

2RA

–

2RB

RA

–

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

=

f

1

t1

t2

+

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

=