What is 555 timer (part-2)

Function of 555 timer-

 So, by this threshold voltage, we are controllingthe output voltage. And same is true with this trigger pin. So, let's say, the voltage at this threshold pin is less than (2/3)Vcc voltage. That means the output of the first comparator is low voltage. Now, whenever this trigger signal goes below this (1/3)Vcc voltage, then the output of the second comparator will become high. So, in this case, S will become 1 and R willbe equal to zero. So, this flip-flop will get set to the logic1. And in a way, the output will also get set to the logic 1.

Image Source - Google | Image by - wikimediacommmons

So, using these threshold and trigger pins actually we are controlling the output voltage. And in a way, we are controlling the timing of this output signal. So, to change the input voltage to this threshold pin, the external resistor and the capacitors are connected between this threshold and the discharge pin through the supply voltage. And the same is true with the trigger signal. Then there is one more pin, using which wecan also control the timing. And that pin is the pin number 5. Thus, this pin is known as the control pin. And it is directly connected to the inverting terminal of the first comparator.

Now, if you see the inverting terminal of this first comparator, there is a reference voltage of (2/3)Vcc applied using this voltage divider circuit. So, by default, the reference voltage to the first comparator is (2/3) Vcc. But it may, utilizing this control pin, we can externally apply some other reference voltage and by which we can change the circumstance of the output signal.So, using this control, threshold and thetrigger pins, we can change the timing of the output signal. Now, as I said before to change the inp[utat this threshold pin, the external resistor and the capacitors are connected between this threshold and the discharge pins. Along these lines, this release pin helps the capacitor in the releasing at whatever point the output is in a low state. So, let's understand how this transistor will help the capacitor in the discharging. So, let's say the output of this 555 timeris 0V. It means that the Q-bar signal will be equalto 1. Because here this output drive circuit isthe inverting circuit.

So, as this Q-bar is 1, the base of this transistor will be at high voltage. So, here this transistor acts like a switch. So, whenever the input to this transistor is logic 1, then it will act as a closed switch. What's more, it will offer an exceptionally low impedance to this capacitor. So, through this path, the capacitor willget discharged. On the other end, whenever this Q-bar is zero,or let's say the output is high, at that time the input to this transistor will be equal to zero. thus, this transistor will go about as an open switch.So, in that case, this transistor will provide a high impedance to this capacitor. And the last pin which is retained is the reset pin. Presently, this reset pin is a functioning low pin. It means that when logic 0 is applied to this pin, then the flip-flop of this 555 timer will get reset.

Image source - Google | image by - Wikimediacommons

Furthermore, as it were, we can say that the output of the 555 timer will likewise get reset.So, irrespective of the working of this 555timer, whenever this reset pin goes low, the output of this 555 timer will become zerovolts. Or we can say that the 555 timer will get reset. Thus, at whatever point this pin isn't in an utilization then it ought to be associated with the supply voltage. So, in this way, in this 555 timer ic, by changing the inputs we can control the timing of the output signal and by connecting the external components like a resistor and the capacitor this 555 timer can be configured either as astable, monostable and bistable multivibrator. So, in the future videos, we will see that by connecting the external components how this 555 timer can be configured either as astable, monostable and the bistable multivibrator.