LM555 データシートの表示（PDF） - Fairchild Semiconductor
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LM555 Datasheet PDF : 14 Pages
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+Vcc
4
8
RA
RESET
Vcc 7
DISCH
2 TRIG
RB
6
Output
THRES
3 OUT
Modulation
GND CONT 5
C
1
LM555/NE555/SA555
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-----C-----–-----V----E--
RE
(12)
Here, VE is
VE
=
VBE
+
--------R----2---------
R1 + R2
VC
C
( 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
9
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