It is a presentation based on I.C. 555 timer and its various mode of operation and its pin configuration is also given and its various application.

1. DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING
PRESENTATION
ON
555 TIMER & ITS APPLICATIONS
Guided by:-
Priyanka Patel
Asst . Prof(ECE)
LIT, Sarigam.
Submitted by:-
Name: Enrollnment No.
Jay Baria 150860111003
Laxmi Institute of Technology, Sarigam
Approved by AICTE, New Delhi; Affiliated to Gujarat Technological University, Ahmedabad

2. WHAT IS THE 555 TIMER?
• The 555 timer is one of the most remarkable integrated circuits ever
developed. It comes in a single or dual package and even low power
cmos versions exist - ICM7555.
• Common part numbers are LM555, NE555, LM556, NE556. The 555
timer consists of two voltage comparators, a bi-stable flip flop, a
discharge transistor, and a resistor divider network.

3. BLOCK DIAGRAM OF TIMER 555 IC

4. • The voltage divider (blue) has three equal 5K resistors. It divides
the input voltage (Vcc) into three equal parts.
• The two comparators (red) are op-amps that compare the
voltages at their inputs and saturate depending upon which is
greater.
• The Threshold Comparator saturates when the voltage at the
Threshold pin (pin 6) is greater than (2/3)Vcc.
• The Trigger Comparator saturates when the voltage at the Trigger
pin (pin 2) is less than (1/3)Vcc
INSIDE THE 555 TIMER

5. • The flip-flop (green) is a bi-stable device. It generates two
values, a “high” value equal to Vcc and a “low” value equal to 0V.
• When the Threshold comparator saturates, the flip flop is Reset (R)
and it outputs a low signal at pin 3.
• When the Trigger comparator saturates, the flip flop is Set (S) and it
outputs a high signal at pin 3.
• The transistor (purple) is being used as a switch, it connects pin
7 (discharge) to ground when it is closed.
• When Q is low, Qbar is high. This closes the transistor switch and
attaches pin 7 to ground.
• When Q is high, Qbar is low. This open the switch and pin 7 is no
longer grounded

6. PIN CONFIGURATIONS OF THE 555 TIMER

7. • Pin Functions - 8 pin package
• Ground (Pin 1)
• Not surprising this pin is connected directly to ground.
• Trigger (Pin 2)
• This pin is the input to the lower comparator and is used to set the latch, which in
turn causes the output to go high.
• Output (Pin 3)
• Output high is about 1.7V less than supply. Output high is capable of Isource up
to 200mA while output low is capable of Isink up to 200mA.
• Reset (Pin 4)
• This is used to reset the latch and return the output to a low state. The reset is an
overriding function. When not used connect to V+.

8. • Control (Pin 5)
• Allows access to the 2/3V+ voltage divider point when the 555 timer is
used in voltage control mode. When not used connect to ground through
a 0.01 uF capacitor.
• Threshold (Pin 6)
• This is an input to the upper comparator.
• Discharge (Pin 7)
• This is the open collector to Q14 in figure 4 below.
• V+ (Pin 8)
• This connects to Vcc and the Philips databook states the ICM7555 cmos
version operates 3V - 16V DC while the NE555 version is 3V - 16V DC.
Note comments about effective supply filtering and bypassing this pin
below under "General considerations with using a 555 timer"

9. TYPES OF 555-TIMER CIRCUITS
• Astable Multivibrator
puts out a continuous
sequence of pulses
 Monostable Multivibrator (or one-
shot) puts out one pulse each time
the switch is connected

10.  IC 555 HAS THREE OPERATING MODES:
1. BISTABLE MODE OR SCHMITT TRIGGER – THE 555 CAN OPERATE AS A FLIP-FLOP, IF
THE DIS PIN IS NOT CONNECTED AND NO CAPACITOR IS USED. USES INCLUDE BOUNCE-
FREE LATCHED SWITCHES.
2. MONOSTABLE MODE – IN THIS MODE, THE 555 FUNCTIONS AS A "ONE-SHOT" PULSE
GENERATOR. APPLICATIONS INCLUDE TIMERS, MISSING PULSE DETECTION, BOUNCE-
FREE SWITCHES, TOUCH SWITCHES, FREQUENCY DIVIDER, CAPACITANCE
MEASUREMENT, PULSE-WIDTH MODULATION (PWM) AND SO ON.
3. ASTABLE (FREE-RUNNING) MODE – THE 555 CAN OPERATE AS AN ELECTRONIC
OSCILLATOR. USES INCLUDE LED AND LAMP FLASHERS, PULSE GENERATION, LOGIC
CLOCKS, TONE GENERATION, SECURITY ALARMS, PULSE POSITION MODULATION AND
SO ON.
OPERATING MODES OF IC

11.  IN BISTABLE (ALSO CALLED SCHMITT TRIGGER) MODE, THE
555 TIMER ACTS AS A BASIC FLIP-FLOP.
 THE TRIGGER AND RESET INPUTS (PINS 2 AND 4
RESPECTIVELY ON A 555) ARE HELD HIGH VIA PULL-UP
RESISTORS WHILE THE THRESHOLD INPUT (PIN 6) IS SIMPLY
FLOATING.
 THUS CONFIGURED, PULLING THE TRIGGER MOMENTARILY
TO GROUND ACTS AS A 'SET' AND TRANSITIONS THE OUTPUT
PIN (PIN 3) TO VCC (HIGH STATE).
 PULLING THE RESET INPUT TO GROUND ACTS AS A 'RESET'
AND TRANSITIONS THE OUTPUT PIN TO GROUND (LOW
STATE). NO TIMING CAPACITORS
 PIN 5 (CONTROL VOLTAGE) IS CONNECTED TO GROUND VIA A
SMALL-VALUE CAPACITOR (USUALLY 0.01 TO 0.1 ΜF). PIN 7
(DISCHARGE) IS LEFT FLOATING
BISTABLE MODE

12.  PULSE GENERATOR CIRCUIT WHICH THE PERIOD IS CALCULATED FROM RC
NETWORK AND CONNECTED TO EXTERNAL OF 555 TIMER
 STABLE WHEN THE OUTPUT LOGIC LOW (LOGIC = 0)
 WHEN A PULSE IS TRIGGER AT PIN 2 (NORMALLY NEGATIVE TRIGGER PULSE),
TIMER OUTPUT WILL CHANGE TO HIGH (+VS) FOR A WHILE AND CHANGE TO
LOW (STABLE CONDITION). THE CONDITION WILL CONTINUE LOW UNTIL PULSE
IS TRIGGER AGAIN.
 THE TIMING PERIOD IS TRIGGERED (STARTED) WHEN TRIGGER INPUT (555 PIN
2) IS LESS THAN 1/3 VS, THIS MAKES THE OUTPUT HIGH (+VS) AND THE
CAPACITOR C1 STARTS TO CHARGE THROUGH RESISTOR R1. ONCE THE TIME
PERIOD HAS STARTED FURTHER TRIGGER PULSES ARE IGNORED.
 THE THRESHOLD INPUT (555 PIN 6) MONITORS THE VOLTAGE ACROSS C1 AND
WHEN THIS REACHES 2/3 VS THE TIME PERIOD OVER AND THE OUTPUT
BECOMES LOW,
 AT THE SAME TIME DISCHARGE (555 PIN 7) IS CONNECTED TO 0V, DISCHARGING
THE CAPACITOR READY FOR THE NEXT TRIGGER.
MONOSTABLE MODE

13. 1
3
+VCC
7
6
2
8
One-shot operation
R
C
1/3 VCC
R
S
input trigger
Discharge
transistor
Q
Inverter
The input trigger resets the flip-flop and C then charges
until the upper comparator trips and sets the flip-flop.

14. ASTABLE MODE
 Astable multivibrators are
also known as Free-
running Multivibrator.
 Astable do not need trigger
pulse for external to change
the output.
 The period for LOW and
HIGH can be calculated
based on resistor and
capacitor value that
connected at outside of
timer.
C charges through RA+ RB
and discharges through RB.

15. 555 TIMER
• At the beginning of the
cycle, C1 is charged
through resistors R1 and
R2. The charging time
constant is
• The voltage reaches
(2/3)Vcc in a time 1)21(693.01arg CRRTt ech 
1)21(arg CRRech 

16. 555 TIMER
• When the voltage on the
capacitor reaches
(2/3)Vcc, a switch (the
transistor) is closed
(grounded) at pin 7.
• The capacitor is
discharged to (1/3)Vcc
through R2 to ground, at
which time the switch is
opened and the cycle
starts over.
1)2(arg CRedisch 
1)2(693.02arg CRTt edisch 

17. 555 TIMER
• The frequency is then given by
f
R R C R R C

 

 
1
0 693 1 2 2 1
144
1 2 2 1. ( )
.
( )

18. Output voltage high
turns off upper LED
and turns on lower
LED
Capacitor is charging through Ra and Rb
Output is high for
0.693(Ra+Rb)C
555 Animation

19.  SCHMITT TRIGGER
 PPM
 PWM
 LINEAR RAMP GENERATOR
 PRECISION TIMING
 PULSE GENERATION
 TIME DELAY GENERATION
 SEQUENTIAL TIMING
 USED AS A QUAD TIMER
APPLICATIONS

20. THANK YOU