IC NE 555 Timer
555 timer IC is the cheap, popular and precise timing device
used in various applications. It gets the name from the three 5KΩ resistors
that are used to generate two comparator reference voltages. This IC is
operated as monostable, bistable or astable multivibrater to produce a variety
of applications.
This IC comes with bipolar 8 pins dual in-line package. It
consists of 25 transistors, 2 diodes and 16 resistors arranged to form two
comparators, flip-flops, and high current output stage.
Pin Description
The following is the Pin Description
Pin 1-Ground: It is connected to ground as usual. For the
timer to function this pin should be connected to ground.
Pin 2-TRIGGER: The negative input comparator No 1. A
negative pulse on this pin “sets” the internal Flip-flop when the voltage drops
below 1/3Vcc causing the output to switch from a “LOW” to a “HIGH” state
Pin 3-OUTPUT: This pin also has no special function. This
pin is drawn from PUSH-PULL configuration formed by transistors.This pin gives
the output.
Pin 4-Reset: There is a flip-flop in the 555 IC timer chip.
The output of flip-flop controls the chip output at pin 3 directly. This pin is
connected to Vcc for the flip-flop to stop from hard resetting.
Pin 5-Control Pin: The control pin is connected from the
negative input pin of comparator one. The function of this pin to give the user
the direct control over the first comparator.
Pin 6-THRESHOLD: Threshold pin voltage determines when to
reset the flip-flop in the timer. The threshold pin is drawn from positive
input of comparator1.
Pin 7-DISCHARGE: The discharge pin is connected directly to
the Collector of an internal NPN transistor which is used to “discharge” the
timing capacitor to ground when the output at pin 3 switches “LOW”.
Pin 8-Power or VCC: This pin also has no special function.
It is connected to a positive voltage.
Working Modes OF 555 Timer IC
The 555 timer IC operates in modes
Astable mode
Monostable mode
Bistable mode
Astable mode
Astable mode means there will be no stable levels at the
output. Thus the output will fluctuate from high and low. This character of the
astable output is used as a clock or square wave output for many applications.
Features of 555 timer IC
It operates from a wide range of power supplies ranging from
+ 5 Volts to + 18 Volts supply voltage.
Sinking or sourcing 200 mA of load current.
The external components should be selected properly so that
the timing intervals can be done in several minutes along with the frequencies
exceeding several hundred kiloHertz.
The output of a 555 timer can drive a transistor-transistor
logic (TTL) due to its high current output.
It has a temperature stability of 50 parts per million (ppm)
per degree Celsius change in temperature, or equivalently 0.005 %/ °C.
The duty cycle of the timer is adjustable.
The maximum power dissipation per package is 600 mW and its
trigger and reset inputs has logic compatibility.
Thus, this is all about making of Blinking LED using a 555
timer IC. We hope that you have got a better understanding of this concept.
Furthermore, any queries regarding this topic or 555 timer based projects,
please give your valuable suggestions by commenting on the comment section
below.
Manmohan Pal
Mob. 8989811397
mannmohanpal@gmail.com
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