Op-Amps, PWM and Ignition Coils Tutorial



In this episode Shahriar discusses methods for generating a pulse-width-modulated (PWM) signal entirely in the analog domain by employing operational-amplifiers (Op-Amps). A total of four op-amps from a single power supply are used in unity-gain negative feedback, astable positive feedback, integrator and open-loop comparator configurations. The theory of operation as well as measurement are also presented. This episode also includes a quiz. Please post your answers in the comment section.

As a final experiment, an ignition coil is used to generate in excess of 20k volts! The combination of the PWM circuit and the ignition coil provides a stand-alone fully analog high voltage power supply.

Part 1:

Part 2:

Part 3:


  1. Daily Dose says:

    Please help me!!!! What IC-s did you use (OP-AMPs)? and could you suggest a model(type of capacitors, resistors) which controls a LED-light with 2.5 Watt Power? 

  2. mjg8t says:

    Awesome content. I would like to see Some sort oftextuall doc that I could reference without having to try and find info in the video. Thbanks for your efforts.

  3. [...] Op-Amps, PWM and Ignition Coils Tutorial (TheSignalPath.com) [...]

  4. radionics says:

    I am really impressed with your writing abilities as neatly as with the structure in your blog. Is that this a paid subject matter or did you customize it yourself? Either way keep up the excellent quality writing, it is uncommon to look a nice weblog like this one today..

  5. Rehan says:


    Great blog, your videos are very entertaining.

    The dielectric strength of air is typically close to 10kv/cm as you say. It’s worth noting that the dielectric strength of air (gases) is not only a function of gas composition, humidity and electrode geometry, it is also non-linear at smaller electrode separations. This effect is nicely characterised by the Paschen curve, and is a function of gas pressure as well.


    If you’re looking for ideas for your next video, can I suggest something to do with RF, PLLs or Heterodyning. Or if you are looking to make a set of videos that relate to each other more, perhaps this series on PWM could lead to a teardown of the typical workings of switchmode power supplies?


  6. Yi Yao says:

    Hi Shahriar,

    Quick question, for the coil driver, should you put a fly back diode between the darlington transistor and ground? Right now, when the transistor goes into the shut off phase of the PWM, the current through the coil is being shut off very abruptly and has no path to draw current from. This can cause a huge voltage spike (or dip) at the output of the darlington pair, especially in this situation where the resistance is very low and equivalent inductance can be very high making a high Q inductor. Could this ever exceed the darlington’s emitter-collector breakdown voltage (and damage the transistor)? I know they put flyback diodes in buck SMPS, but I have always thought that it was for the sake of efficiency. Is this necessary or is this a matter of efficiency or component safety?

    I remember you were my ECE331 TA (I don’t remember the exact course code). That course had some good labs. I saw your blog recommended by Google ready and was surprised to find you here. Everything looks pretty good, there’s no shortage of interesting information for people new for familiar to this.

  7. Jeff says:

    Your video is awesome!! Thanks for the sharing. It’s helpful. I love the last part of this one!

  8. kmmankad says:

    Could you do a video on the 555? Its a highly versatile device,and a lot of basic concepts can be linked back to it.

    • Zac says:

      During my first year of undergrad education I created the same result as the video’s circuit using one opamp and a 555 timer! (analog is fun!)

      I’d like to see some videos explaining the implementation of mathematical functions in real circuits (e.g. how to make a differentiator or integrator) and how to translate between theoretical equations and implemented circuits.

      Maybe a video that implements several mathematical functions?

  9. Shayan Shahramian says:

    A Good application of PWM circuits is in switch mode power supplies. One example of a switch mode power supply would be to convert a low voltage to a higher voltage (boost converter), and depending on the pulse width of the PWM the ratio of output to input voltage is determined.

  10. Kelvin says:

    Explanation is at the right level, i.e. not too detailed and yet informative. This is certainly a webpage worth spreading. Love to see more. Keep up the good work.

  11. rfarrelly says:

    I have realized over the past few years that engineering education is at least 51% communication and how teachers convey the point effectively. That’s something I feel is understated here in Belfast, Northern Ireland at least.

    Thanks Shahriar

  12. rfarrelly says:

    It is rare to find such quality on the web, your vids are definitely up there with EEVBlog, Khan Academy and the likes. Ya just need to keep that content streaming in.

    By the way, it is fascinating for a an EE student like myself to see schematic, theory and output presented so perfectly as mathematics and the application in engineering are often disjointed in class.

    So i am all in favour of more maths such as described in your latest videos on Op amps, PWM and ignition coils.

    Good stuff lad

    • Shahriar says:

      Thank you for the kind comments and feedback.

      I typically try to produce these videos in the same style as how I teach at university. Begin with an idea, look at it mathematically, come up with circuits to perform the desired functions, analyze the circuit theoretically and finally measure the circuit to ensure it operates as predicted/desired. The full cycle!

      • pete says:

        As a self taught hobbyist, I greatly appreciate your videos. Though I have taken college level calculus, it would perhaps be more beneficial for a wider audience to first explain the circuit’s theory of operation from a non mathematical view and reinforce it by looking at it again mathematically just before taking measurements.

  13. Answer to first op-amp: You are using it as a high impedance voltage follower to split your single power supply into a plus and minus dual source.

    Details: Your single power supply source will be feed into a 50/50 voltage divider circuit with relatively high resistance to keep the voltage divider’s current to a minim. Then this divided voltage is feed into the first op-amp’s non-inverting terminal. The out of this op-amp is feed back into the inverting terminal with a short creating wait is called a voltage follower. The output of this op-amp then becomes your new common for the other three op-amps.

    Results: This makes the single source power supply’s ground look like a minus voltage supply and the positive looks like 1/2 the original positive supply to the part of the circuit using the voltage follower’s output as common. From this you can power your other op-amps with equal + and – power rails. What do I win?

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