20 555 timer
TRANSCRIPT
555 Timer
Pin configuration The 555 timer consists of;The 555 timer consists of;
Two voltage comparatorsTwo voltage comparators A bi-stable flip flopA bi-stable flip flop A discharge transistorA discharge transistor and a resistor divider network.and a resistor divider network.
Internal Circuit Of 555 Timer
VA
VB
OutputOutput
Threshold Threshold
Control Control VoltageVoltage
TriggerTrigger
DischargeDischarge
ResetResetVCC
Voltage DividerVoltage DividerComparatorComparator
RS-RS-FFFF
DischargeDischargeTransistorTransistor GND
+ +C1
+ +C2
Q
QRD
SD
5KΩ
5KΩ
5KΩ
T
22
44
5
66
77
88
33
11
<2/3 VCC <1/3 VCC 1 0
>2/3 VCC >1/3 VCC 0 1
<2/3 VCC >1/3 VCC 1 1
>2/3 VCC <1/3 VCC 0 0
RD SDV6 V2
The result for The result for comparingcomparing
1/3 VCCNot permitted
2/3 VCC
+ +C1
+ +C2
.
.
5KΩ
5KΩ
5KΩ
VA
VB
VCC
RD
SD
5
6
2
VV66 VV22
<2/3 <2/3 UUCCCC <1/3 <1/3 UUCCCC
>2/3 >2/3 UUCCCC >1/3 >1/3 UUCCCC
<2/3 <2/3 UUCCCC >1/3 >1/3 UUCCCC
QQ TT
11
00
保持保持
onon
offoff
保持保持
Q
QRD
SD
Toutpoutp
utut
RRDD SSDD
11 00
1100
11 11
QQ TT
11
00
remainremain
onon
offoff
remainremain
remainremain remainremain
Monostable Multivibrator & Waveforms
Monostable Multivibrator (One-shot) OperationMonostable Multivibrator (One-shot) Operation
(grand)
uC
R1
+V+VCCCC
ui
VVCCCC
+ +C1
+ +C2
QQRD
SD
5KΩ
5KΩ
5KΩ
VA
VB
T
1
3
48 (Re)
uO
65
2
7
>2/3 VCC
0
1 1 0
1
Q=0
on
1 Steady stateSteady state
(grand)
uC
R1
+V+VCCCC
ui
VVCCCC
+ +C1
+ +C2
QQRD
SD
5KΩ
5KΩ
5KΩ
VA
VB
T
1
3
48 (reset)
uO
65
2
7
1
1 0
1
Q=1
off
Transiet stateTransiet state
0
< 1/3 UCC
0
0
1
Monostable Monostable MultivibratorMultivibrator (One-shot) Operation (One-shot) Operation
Monostable Multivibrator(One-shot) OperationMonostable Multivibrator(One-shot) Operation
(grand)
uc
R1
+V+VCCCC
ui
VVCCCC
+ +C1
+ +C2
QQRD
SD
5KΩ
5KΩ
5KΩ
VA
VB
T
1
3
48 (reset)
uO
65
2
7
>2/3 VCC
1
0 1
0
Q=1
0
1 01
1
0
Steady stateSteady state
Q=0
ui
tuC
tuO
ttp =RC ln3=1.1RC
2/3UCC
What is a monostable multivibrator?
•With one stable state
•Normally in its stable state,to change to its unstable state only when triggered
•Once triggered,to remain in its unstable state for a predetermined length of time and then return to its stable state automatically
Astable Multivibrator & Waveforms
UCC
+ +C1
+ +C2
QQRD
SD
.
.
.
5KΩ
5KΩ
5KΩ
VA
VB
T
1
32
4
56
7
8
(grand)
uO
2) Astable Multivibrator(Oscillator)2) Astable Multivibrator(Oscillator)
firstfirstuuCC=0=0
0
1
11
0
0
>2/3 UCC
RD=1
SD=0
.
.
uC
R1
R2
.+
–
charge
discharge
1
<1/3 UCC
485627 1
3
+VCC
uO
.
uC..
C
R1
R2
ttp1p1 =(=(RR11++RR22))CC ln2=0.7( ln2=0.7(RR11++RR22))CCttp2p2 ==RR22CC ln2=0.7 ln2=0.7RR22CC
TT==ttp1p1++ttp2p2 =0.7(=0.7(RR11+2+2RR22))CC
tp1 tp2
2/3UCC
1/3UCC
uC
t
uO
t
What is an astable multivibrator?Duty Cycle = ttp1p1/T/T
Applications using 555 timer
A light dimmer ; A car tachometer Traffic Lights ; Infra Red (IR) remote control ;