INTRODUCTION TO 555 IC

        555 is the one of the most popular ic among the electronic hobbyist.It's also called as timer ic.The 555 is a highly stable controller capable of  producing accurate timing pulses.With the monostable operation,the time delay is controlled by one external resistor and one  capacitor.While with the astable operation the frequency and duty cycle controlled by two resistors and one capacitor.There eight pins in 555ic.


PIN CONFIGURATIONS

• PIN1:-Ground

• PIN2:-It's the trigger pin.It detect 1/3v of vcc and make the output of 555 is high.

PIN2 has a control over PIN6.If PIN2 and PIN6 is low o/p goes and stay as HIGH.If PIN6 is high and PIN2 is low then output goes LOW.

• PIN3:-It's the output pin of the 555 ic.Note the point that the output of the 555 ic is 1-2v less than the vcc.For example,if the vcc is 5v,then the output voltage of the 555 is become 3v.

• PIN4:-It's the RESET pin of the 555.RESET pin is internally connected to high via 100k resistance and it must be taken below 0.8v to reset the chip.

• PIN5:-It's the CONTROL pin of the 555.A votage applied to this pin will change the timing of RC network by changing the reference voltage of the two comparator of the 555 ic.

• PIN6:-THRESHOLD pin.It detect 2/3v of rail and make output low only if PIN2 is high.

• PIN7:-It's the DISCHARGE pin.It goes LOW when PIN6 detect 2/3v but PIN2 must be high.

If PIN2 is high,then PIN6 can high or low and PIN7 remains low.PIN7 goes open and stay high when PIN2 detect 1/3v of vcc and PIN6 is low.

Here,we noted that PIN7 is almost like the PIN3 but PIN7 does not go HIGH instead it goes OPEN.But it goes low and can sink upto 200mA.

• PIN8:-It's the supply pin.Connect it to the positive rail.

 

PIN-OUT OF 555

Schematic diagram

Just take a look at the above image.We can see that there two comparators,one is in inverting and other one is in non-inverting mode.These two comparator get reference voltage via the three resistors(R=5k).So now you may get,why is it called as a 555 IC..There three 5k resistors in 555.


In the next post, we focus on monostable,astable, and also how we can make different circuits by using 555 for different purpose.


SALAM!. :)...