555 Timer IC PWM (Pulse Width Modulation) Generator Circuit on Proteus

555 Timer IC PWM (pulse width modulation) Generator Circuit

555 Timer IC PWM (Pulse Width Modulation) Generator Circuit on Proteus electrobuff.blogspot.com

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555 Timer IC Basics: Pinout, Astable, Monostable, Bistable Mode, PWM Circuit, Equivalent ICs

555 Timer IC Pinout, DIP Package electrobuff.blogspot.com

555 Timer IC

555 Timer IC Pinout

555 Timer Pinout Configuration

Pin Number	Pin Name	Description
1	Ground	Ground Reference Voltage 0V
2	Trigger	Responsible for transition of the flip-flop from set to reset. The output of the timer depends 2 I on the amplitude of the external trigger pulse applied to this pin
3	Output	This pin is normally connected to load as it is the only pin with output driven waveform
4	Reset	Negative pulse applied to this pin to disable or reset the timer. When not used for reset 4 I purposes, it should be connected to VCC to avoid false triggering
5	Control	Controls the threshold and trigger levels. It determines the pulse width of the output 5 Voltage I waveform. An external voltage applied to this pin can also be used to modulate the output waveform
6	Threshold	Compares the voltage applied to the terminal with a reference voltage of 2/3 Vcc. The 6 I amplitude of voltage applied to this terminal is responsible for the set state of the flip-flop
7	Discharge	Open collector output which discharges a capacitor between intervals (in phase with output). 7 I It toggles the output from high to low when voltage reaches 2/3 of the supply voltage
8	Vcc	Supply Voltage (Typical = 5V, Maximum = 18V)

555 Timer IC Features

Typical operating voltage is +5V, can withstand a maximum of +18V.
The source/sink current of the output pin is 200mA
Consumes up to 3mA when operating at +5V
Trigger Voltage is 1.67 when operating at +5V
Operating Temperature is 70 degree Celsius.
Available in 8-pin PDIP, SOIC, and VSSOP packages

555 Timer IC Equivalent

LM556, NE556

Brief Description on 555 Timer ICs

555 Timer IC is the most commonly used ICs for timing and Pulse generation applications. They can adopt itself into various applications due to its different operating modes. They are very simple to understand if we take a look at the components present inside as shown below

555 Timer IC internal Block Diagram Structure electrobuff.blogspot.com

There are three resistors of value 5K, which gives this IC it’s iconic name “555 Timer”. It has dual comparators and flip-flop which will make this IC operated in three different modes such as Astable, Monostable and Bistable(Schimitt) Mode.

555 Timer IC Astable Mode:

In this mode a square wave is produced at the output pin. This wave is usually used to turn ON and OFF a load at specific intervals like, blinking a LED. This mode is also used to generate clock pulse signals for digital IC’s. The ON time (T1) and OFF time (T2) of the wave can be controlled by the Resistors (RA, RB) and Capacitor (C) shown in below figure

555 Timer IC astable circuit diagram .electrobuff.blogspot.com

Monostable Mode:

In Monostable mode a pulse of pre-defined length is produced when a trigger button is pressed. The output pin stays low until the button is pressed and once pressed it remains high for a period of time decided by the value of resistor (RA) and Capacitor (C) shown in the below circuit.

555 Timer IC bistable circuit diagram .electrobuff.blogspot.com

Bi-Stable Mode:

The Bi-stable mode is also called as Schmitt Trigger Mode. This mode is used when a load has to be turned on and off using a push button.

The 555 timer in bistable mode is also known as a flip-flop circuit. A flip-flop circuit alternates between two stable states, in this case the output of electrical current from the output pin. Unlike the monostable mode and astable modes, bistable mode doesn’t need a resistor and capacitor to set the timing of the circuit. In fact there is no timing in this circuit. There are only two stable states (on and off) controlled directly by the trigger pin and reset pin.

This mode does not have major practical importance hence it is rarely used.

I’ll demonstrate the bistable mode of the 555 timer with an LED and push buttons connected to the trigger pin and reset pin. Pressing the trigger button once will make the LED turn on and stay on. Pressing the reset button will make the LED turn off and stay off.

555 Timer IC Bistable Mode Circuit Diagram electrobuff.blogspot.com

Pressing the trigger button allows current to flow from Vcc to ground, which causes the voltage at the trigger pin to drop. As we saw in the monostable mode article, when the trigger pin is at a low voltage, the output gets switched on and the LED lights up. The output stays on until the voltage at the threshold pin goes above 2/3 Vcc. Since the threshold pin is wired to ground in this circuit, it never reaches 2/3 Vcc, so the output stays on indefinitely.

Now if the reset button is pressed, the voltage at the reset pin flows to ground and the pin goes low. When the reset pin goes low, the output is switched off.