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L12, 555 Timer IC

Designed and invented by Hans R. Camenzind, the 555 timer chip is an integrated circuit (IC) chip that has the versatility to handle multi-vibrator and timer applications. It can include over 20 transistors, 15 resistors and 2 diodes in one 8-pin chip, depending on the company that manufactures it.

The 555 timer have three main operating modes, namely Astable Monostable and Bistable. Each mode denotes a different type of circuit that has a specific output. The 555 timer chip can be used as an oscillator, the flip-flop element and it provides time delays.


555 Timer pin configuration

A simplified “pin configuration” signifying the internal circuitry of the IC 555 timer is given below with a brief description of each of its connecting pins to give a clearer understanding of how it works.

Pin 1: Ground – the ground for the chip

Pin 2: Triggers – triggers the input signal and starts the waveform.

Pin 3: Output – where signal is outputted

Pin 4: Reset terminal – forces the output to zero volts

Pin 5: Control voltage

Pin 6: Threshold – resets output waveform to zero volts

Pin 7: Discharge – discharges the capacitor charge to zero volts

Pin 8: Power – where the chip gets power

Modes of 555 Timer-

555 timer has three operating modes, namely astable mode, monostable mode & bistable mode.


In this mode, 555 Timer can work as an oscillator. Uses contain LED & lamp flashers, logic clocks, pulse generation, security alarms, tone generation and PPM and so on. The 555 timer IC can be used as a simple analog to digital converter. For example, selecting a thermistor as a timing resistor permits the use of the 555 timer IC in a temperature sensor, the o/p pulse period is determined by the temperature.


In this mode, the 555 timer IC can work as a flip-flop, if the DIS-pin is not connected & no capacitor is used. It is used in bounce-free latched switches.


In this mode, 555 timer IC works as a one shot pulse generator. Applications mainly include bounce free switches, timers, touch switches, missing pulse detection, frequency divider, pulse-width modulation (PWM), capacitance measurement, and so on.

Applications of 555-

· 555. timer IC works from a wide range of power supplies ranging from +5V to +18V.

· Sourcing or sinking load current is 200mA.

· The external components must be selected correctly, so that the timing intervals can be completed in several minutes along with the frequencies beyond several hundred kHz.

· The o/p of a 555 timer IC can drive TTl due to its high current o/p.

· The timer’s duty cycle is adjustable.

· The max power dissipation per package is 600 mill watts & its reset and trigger i/phas logic compatibility.

555 Timer circuit-

The 555 timer ICs are used to generate a precise square wave form and that is used in many circuits. This circuit is designed with transistors, diodes, resistors and flip flops, and this circuit can be worked in the range of 4.5-15V DC supply. The 555 timer circuit consists of three functional parts, namely flip-flops, a comparator and a voltage divider

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