555 Timer

1
555 Timer
2
Pin configuration

• The 555 timer consists of
• Two voltage comparators
• A bi-stable flip flop
• A discharge transistor
• and a resistor divider network.

3
Internal Circuit Of 555 Timer
4
VCC
Reset
Control Voltage
VA
Threshold
Output
Trigger
VB
Discharge
DischargeTransistor
GND
RS-FF
Voltage Divider
Comparator
5
The result for comparing
2/3 VCC
Not permitted
1/3 VCC
6
RD
SD
Q
T
1
0
1
off
1
0
0
on
remain
1
1
remain
remain
remain
7
Monostable Multivibrator Waveforms
8
Monostable Multivibrator (One-shot) Operation
Steady state
0
1
1
Q0
gt2/3 VCC
(grand)
on
9
Monostable Multivibrator (One-shot) Operation
Transiet state
0
Q1
lt 1/3 UCC
(grand)
off
10
Monostable Multivibrator(One-shot) Operation
Steady state
1
Q1
gt2/3 VCC
(grand)
11
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

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Astable Multivibrator Waveforms
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2) Astable Multivibrator(Oscillator)
charge
1
gt2/3 UCC
lt1/3 UCC
first uC0
1
discharge
14
What is an astable multivibrator?
Duty Cycle tp1/T

• With one stable state

15
Applications using 555 timer

• A light dimmer
• A car tachometer
• Traffic Lights
• Infra Red (IR) remote control