Introduction: Simple PWM Generator
this instructable will show you a neat little circuit to generate PWM (Pulse Width Modulation), that is quick and easily built from components that are likely to be in your collection already!
Parts List:
- 1x 555 Timer IC
- 1x 100K Linear Pot
- 1x 100nF Capacitor (Ceramic or Propylene Film)
- 1x 10nF Capacitor (Ceramic or Propylene Film)
- 2x small signal diodes (1N4148/1N5818 etc)
- A 12V DC Power Source
The frequency of the output is dependant on the values of R1 (the pot) and C1. If you require a specific frequency, you can work it out using the following formula:
Frequency = 1.44 / (R1 * C1)
In order to drive inductive loads (motors, solenoids etc.) it is highly recommended to add a transistor/MOSFET onto pin 7 (the PWM output) -- don't forget a free-wheel diode if you do!
If you require finer adjustment of the PWM output you can always add a low value pot in series with R1 (suggested value is ~5K linear).
10 Comments
6 years ago
Hi, i want to use in for a HHO generator, is it possible.
Reply 6 years ago
Hi,
This wouldn't be suitable for a HHO generator as it can not provide enough current to support electrolysis nor is it at a fast enough frequency
Reply 6 years ago
Thanks fir the quick response, do you perhaps have any ideas for me that would be suitable?
7 years ago
I have a feeling you are missing a THR connection... Maybe a short to TRIG?
Reply 7 years ago
Nope, no THR connection required
Reply 7 years ago
Trg and Thr are internally connected to the comparators that set and reset the output. When Vtrg < 1/3 Vcc the output flip-flop is set. When Vthr > 2/3 Vcc the output is cleared. How is this circuit supposed to clear it's output with no thr connection?
Reply 7 years ago
My apologies, I haven't looked at this circuit in a while - you are correct, connect THR to TRG
7 years ago on Introduction
Do you have another design for that just with a 10K pot?
Reply 7 years ago on Introduction
If you replace the 100K pot with a 10K pot, you'll have to times the value of C1 by 10 - replace C1 with a 1uF capacitor, electrolytic doesn't matter.
7 years ago on Introduction
Nice design.