555 Timer IC and how it works Explained

 How a 555 Timer magic IC works

555 Timer IC Pinout and Internal Block Diagram

Introduction:

The 555 timer IC is a versatile integrated circuit widely used in electronics as a timer, pulse generator, and oscillator. The 555 timer IC is a powerful and widely used component in electronic circuits, providing a reliable and easy-to-use solution for various timing applications.

The 555 timer is an integrated circuit (IC) widely used in electronics for various timing and pulse generation applications. Introduced in 1972 by Signetics (now a part of ON Semiconductor), the 555 timer has become a staple component in countless electronic circuits due to its versatility and ease of use. Its three operating modes, astable, monostable, and bistable, make it suitable for a wide range of applications.

The 555 timer's enduring popularity is attributed to its simplicity, reliability, and versatility, making it a fundamental building block in electronic design for both beginners and experienced engineers.

Below is a tutorial explaining how the 555 timer IC works, its pinout, and their functions.

Understanding the 555 Timer IC:

Pinout:

The 555 timer IC typically comes in an 8-pin dual in-line package (DIP). The pins are labeled as follows:

 

555 Timer IC Pinout

GND (Pin 1):

Ground: Connect to the ground reference of the circuit.

 

TRIG (Pin 2):

Trigger: Used to trigger the 555 timer by applying a voltage lower than 1/3 of the supply voltage.

 

OUT (Pin 3):

Output: The pulse or square wave output of the 555 timer.

 

RESET (Pin 4):

Reset: Active-low input that resets the internal flip-flop when pulled low. Usually connected to VCC for normal operation.

 

CTRL (Pin 5):

Control Voltage: Used to provide an external voltage reference for the internal comparators. It influences the threshold and trigger levels.

 

THR (Pin 6):

Threshold: The inverting input of the internal comparator. When the voltage at this pin exceeds 2/3 of the supply voltage, the output is switched.

 

DISCH (Pin 7):

Discharge: Used to discharge the timing capacitor to ground when the output is low.

 

VCC (Pin 8):

Positive Supply Voltage: Connect to the positive supply voltage of the circuit.

 Design, Construction, Architecture & Working

The IC 555 timer is a chip used in various areas and applications like pulse generation, an oscillator, and a timer. The 555 Timer is designed using 25 transistors, 2 diodes and 15 resistors.

555 Timer IC internal architecture design with 24 BJT transistors

The functional parts of the 555 timer IC include a flip-flop, voltage divider & a comparator altogether. The main function of this IC is to generate an accurate timing pulse for operating various devices and electronic components.

Internal Block Diagram:

The 555 timer consists of two voltage comparators, an SR flip-flop, a discharge transistor, and a resistor divider network. The internal block diagram is as follows:

 

555 Timer IC internal Block Diagram

Voltage Comparators (Upper and Lower):

The upper comparator monitors the voltage at the THR pin.

The lower comparator monitors the voltage at the TRIG pin.

 

SR Flip-Flop:

The flip-flop controls the state of the output.

 

Discharge Transistor:

Connected to the DISCH pin, it discharges the timing capacitor to ground.

 

Resistor Divider Network:

5kilo Ohm resistors connected between VCC and GND, it provides voltage references for the comparators.

How It Works:

 

Astable Mode (Oscillator):

555 timer IC Astable mode circuit

Connect the TRIG and THR pins.

Connect a resistor (R1) from VCC to the CTRL pin.

Connect a capacitor (C1) from CTRL to GND.

The OUT pin generates a continuous square wave.

555 timer ic astable mode signal waveforms

 

Functions as an oscillator, generating a continuous square wave output.

Commonly used for applications such as LED flashers, tone generators, and clock pulses.

Monostable Mode (One-Shot):

555 timer IC monostable circuit

Connect the TRIG and THR pins.

Connect a resistor (R1) from VCC to the CTRL pin.

Connect a capacitor (C1) from CTRL to GND.

Apply a trigger pulse to the TRIG pin.

The OUT pin produces a single pulse.

555 timer IC monostable signal waveforms

 

Operates as a one-shot timer, producing a single output pulse in response to a trigger.

Widely applied in applications like pulse-width modulation, time-delay circuits, and touch-sensitive switches.

Bistable Mode (Flip-Flop):

555 timer IC bistable mode circuit

Connect TRIG to THR internally.

Connect a resistor (R1) from VCC to the CTRL pin.

Connect a capacitor (C1) from CTRL to GND.

Use an external trigger to set and reset the flip-flop.

555 timer ic bistable mode signal waveforms

 

Functions as a flip-flop, allowing for the storage of binary information.

Used in toggling applications, such as flip-flop circuits, where external triggers can set or reset the output state.

Example Formulas:

Frequency in Astable Mode:

f = 1.44 / ((R1 + 2*R2) * C1)

Pulse Width in Monostable Mode:

t=1.1⋅R⋅C

 

Typical Applications:

 The 555 timer is one of the most widely used integrated chips in digital electronics. Some common uses and application of 555 timers IC are as follows:

• It is used for Pulse, Waveform, and square wave generation.
• It is also used in time delay generation, precision timing, and sequential timing.
• It can be used as a mono-stable multi-vibrator and a-stable multi-vibrator.
• It is mostly used in PWM (Pulse Width Modulation) & PPM (Pulse Position Modulation).
• Used in Tachometers & temperature measurement.
• Commonly used in DC Voltage Regulators.
• Used for conversion like Voltage to Frequency Converter.
• It is also used in Frequency Divider.
• It is used in the Pulse detector.
• It can be used to design a Timer Switch.

. used in educational settings to teach basic electronics principles due to its straightforward design 

  and multiple applications.