# 555 timer Pulse Generator circuits | astable mode

This is a pulse generator circuits or standard Astable Multivibrator oscillator or free running circuit using IC555 timer, NE555, LM555 . We use it for digital Logic circuits. IC-555 is popular easy to use small size with 8 pins. It is combining analog and digital chip. Basic using it need the voltage supply 5V to 15V, Maximum supply voltage 16v – 18v, Current consumption  about 10mA, Maximum Output Current is 200mA. Maximum  frequency  output is 500kHz.

There are many ways to use the IC555.  We can use  them in three different types of oscillators:
(1)Astable Multivibrator oscillator
If frequencies  more than 1 cycle per second, it is an oscillator (pulse generator or square wave oscillator).
But frequencies lower than 1 cycle per second it is TIME DELAY.
(2) Monostable (ONE SHOT) changes state only once per trigger pulse
(3) Voltage Controlled Oscillator (VCO)

Now we will learn about pulse generator with IC-555 below basic circuit.

### Simple 555 timer astable oscillator circuit

In the circuit above. First of all the current from the power supply flow to the capacitor-C1 charges via the Resistor-R1 and R2, then the voltage in the capacitor reaches 2/3 of the supply voltage, pin 6 detects  this voltage, cause pin 7 cut off this voltage to Ground(0v).
Thus the capacitor-C1 discharges through the resistor-R2 until its voltage is 1/3 of the supply and pin 2 detects this voltage and pin 7 not connect (turns off).  The C1 will charge and voltage across it grow up  again to repeat the cycle.

The top resistor prevent pin 7  may damage as it shorts to 0v when pin 6 detects 2/3 supply voltage.
Its resistance is smaller than R2 and does not come into the timing of the oscillator.

The output frequency will be approximately 1kHz and the duty cycle 50-50,
The Frequency output (F) = 1/{(R1+2R2)*C1}.

The values units in the formula in ohms, farads, seconds and hertz. This formula is much simpler than that of the previous circuit.

Suppose R1 = 1k, R2 = 10k and C = 0.1uF  The result is approx 900Hz

#### Parts you will need

R1: 100K 1/4W Resistors tolerance: 5%
VR1: 1M Potmeter
C1,C2: 0.01uF 50V Ceramic Capacitors
IC1: NE555 Timer

We use simple 555 pulse generator idea to builds many circuits for example below

## High Power 555 Pulse Generator

If you are looking for a pulse oscillator in high current. This is a high power pulse generator circuit that you may like it.

Which the main component is IC-555 timer as the oscillator, and the LM350T provides a high current up to 3A max.

How it works

As you see in Simple Pulse Generator. Which it has a normal current of 200mA maximum only.

However, you can increase the current output up to 3A.

In the first time, we think to use the power transistor-2N3055 (popular coponent in all time) to increase current up.

But we have the better choice, to use other IC, LM350T. It is DC regulator at 3A current, so higher performance than 2N3055 exactly.

In the figure below, we still use the NE555 as the integrated circuit to generate a Square wave Oscillator.

Which we can adjust the frequency output with rotate a VR1-100K. Then, the signal comes out of the output pin go to the pre-driver, transistor-2N2222. To control adj lead of IC LM350T works.

While there is the high voltage comes out of the output, in high current pulse about 3A.

Thus, friends change the value of R5 for controlling the level voltage output in minimum 1.25V to high voltage at around 15V.

Because of this circuit uses input (voltage of power supply about 5V – 15V)

The other ideas, if you want the current just only 1A output. You can use LM317T that it is cheaper than LM350T.

## Pulse generator control frequency using digital IC

This circuit make pulse signal in continuity. We call it that Astable Multi Vibrator circuit. The 555 timer-IC1 is working with VR1, R1, R2, and CT. The value of CT in the selection of the electronic switch circuit IC2 number 4066.Electronic switch with 4 built-in IC 2.

The control the electrical contact switches (ON), The input voltage is positive or logic “1” to the control pin. The pin 13, 5, 6 or 12.

If the control pin to ground. Switch is turned off (OFF). Switches each, to separate the work independently, not be sorted.
And incoming (IN) and output (OUT) can be interchangeable.

It is therefore reasonable to switch the value of C values.With the input signal to the logic of digital circuits,The binary code is “0” to “1”.

When I switch on the control of either a logic “1”, the electrical contact of the switch, then tap it. A capacitor connected to the pin switch is connected to pins 2 and 6 of IC1. To determine the frequency with VR1, R1 and R2.

Sometimes it may be the control logic “1” rather than a pin. Makes the capacitor is connected in parallel, rather than an option. The capacity will be increased. The introduction of the C together. Circuit can reduce or increase the value of R1, R2. Or for convenience, you can adjust the resistance of VR1 at all. Signal pulse is sent out to pin 3 of IC1’s output signal. To enter the circuit, such as count circuit, divide, or be connected to the speaker. To make a sound or signal.

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