# IC 555 generates a PWM signal

Here is a very simple ic 555 oscillator that generates a PWM signal. in this case, i am using a 2n3904 NPN transistor (Q1) as a switch to turn an led on and off. you can also use this to run a dc motor or other heavy load hardware. make sure you use a switching transistor that can handle the voltage and the current you require.you can pretty much use this circuit anywhere because with some modification, you can change the duty cycle limit and such,so i include a link at the end of this article for a ic555 calculator so you can modify this circuit to perfection.

What you will need:

• 555 timer chip, it can be any variation of the chip like the ne555 or lm555.
• 2x 0.1uf (micro Farads) ceramic capacitors.
• 0.01uf (micro Farads) ceramic capacitor.
• 200k R(kilo ohms) potentiometer ( or equivalent resistor voltage divider)
• 10k R (killo ohms)
• 350R resistor
• 2n3904 npn transistorled with your choice of colour
• 2x 1n5818 Schottky Rectifier diods

Notes:
this circuit requires +3v min to +15v max input voltage. this circuit can have a seperate voltage source than the one used by the load (led), but as always they need to have a common ground.
Discharge pin on the 555 is the signal output.

Q1 can handle up to 200ma but anything higher than that and you will get magic smoke. always check your data sheet for your components limitations.
for example 200ma = 10 leds that require 20ma of current each
Q1 can be replaced with other transistors or even mosfet like tip31.

R3 and R4 act as a potentiometer as LTspice simulator does not have a potentiometer model. just use a 200k potentiometer. the potentiometer will act like a voltage divider.

D1 and D2 are the 1n5818, make sure they are pointing to opposite direction of each other.

Results:
as you can see in the pictures below, the circuit is producing PWM signals. fist picture is full duty cycle, second picture is half.

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