KA555I Datasheet, PDF (9/14 Pages) Fairchild Semiconductor – Single Timer

+Vcc
4
8
R_A
RESET
Vcc ₇
DISCH
2 TRIG
R_B
6
Output
THRES
3 OUT
Modulation
GND ^{CONT 5}
C
1
KA555
Figure 11. Circuit for Pulse Position Modulation
Figure 12. Waveforms of pulse position modulation
6. Linear Ramp
When the pull-up resistor RA in the monostable circuit shown in Figure 1 is replaced with constant current source, the VC1
increases linearly, generating a linear ramp. Figure 13 shows the linear ramp generating circuit and Figure 14 illustrates the
generated linear ramp waveforms.
+Vcc
4
RESET
2 TRIG
8
Vcc
DISCH ⁷
Output
3 OUT
THRES ⁶
GND
1
CONT 5
RE ^R1
Q1
R2
C1
C2
Figure 13. Circuit for Linear Ramp
Figure 14. Waveforms of Linear Ramp
In Figure 13, current source is created by PNP transistor Q1 and resistor R1, R2, and RE.
IC = ^V−−−^C−−−^CR−−−_E^–−−−^V−−−^E−
(12)
Here, VE _is
VE = VBE + _R−−−₁−−^R−₊−−²âˆ’_R−−−₂−VCC
( 13 )
For example, if Vcc=15V, RE=20kΩ, R1=5kW, R2=10kΩ, and VBE=0.7V,
VE=0.7V+10V=10.7V
Ic=(15-10.7)/20k=0.215mA
When the trigger starts in a timer configured as shown in Figure 13, the current flowing through capacitor C1 becomes a
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