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I am trying to make a circuit for controlling a spark plug using 555 IC.I found two circuits on the forum which are very similar to each other but from what I have observed, they are using different diodes and I want to know the difference they would make on my circuit. As it can be seen in circuit 2, they are using two IN4148 diodes while the other just uses BYQ28E-200 diode array which I am unsure what it does to the circuit. It is to be noted that circuit-2 works for 1 minute and the MOSFET is heating (slowly), it uses a snubber circuit to protect against voltage spikes but it doesn't really seem conventional to be using the two IN4148 diodes because they might not allow the current to flow. My question is, does the BYQ28E-200 diode array would work the same way as two IN4148 diodes in this circuit configuration? What really is the purpose for a diode array in this? I am trying to see if I even need it after all for what I am trying to achieve. Thanks.

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  • \$\begingroup\$ You'll get a better response if you embed the image into your post. Make it easy for your readers. Add a paragraph break or two for readability. (2 × Enter.) \$\endgroup\$
    – Transistor
    Commented May 18, 2021 at 16:20
  • \$\begingroup\$ The diodes have wildly different voltage/current/speeds. You should really ask the people who designed the circuits why they designed them like they are - most likely random hobbyists use random parts they found somewhere, so there may not be any profound reason why these specific parts are used, or even a way to know if they are suitable or not as people use different coils and the coil parameters are unknown too. \$\endgroup\$
    – Justme
    Commented May 18, 2021 at 16:34
  • \$\begingroup\$ Thanks for the heads up. I am relatively new here so slowly learning haha \$\endgroup\$
    – hello_world07
    Commented May 18, 2021 at 16:39
  • \$\begingroup\$ Check the gate drive, I believe it is being under driven causing the MOSFET to heat. \$\endgroup\$
    – Gil
    Commented May 18, 2021 at 19:21

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The two different diodes are operating in exactly the same way. The 1N4148 diodes are simply two parts, whereas the BYQ28E-200 is a single part. The latter is also able to handle much more power compared to the 1N4148 glass diodes. While they will both "work", I'm not sure how long a 1N4148 would last in this application, they are more of a small signal diode, not meant for large currents.

The differences in the snubber (RC connected to the diodes in question) is most likely related to the schematic author's specific ignition coil. There are hundreds of different ones out there and each one of these was optimized for the coil in use.

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