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| Delay timer using mosfet |
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| paulhm81:
Hello I'm trying to figure out if there is a way to use the schematic in the picture to cut power but not gradually. I would like to avoid using a relay because they are big and my load will be small (0.2amps) and I would also like to avoid microcontrolers or timers. In my car I have an ionizer and my cigarette lighter is always powered. I thought about changing it to work on contact but the ionizer needs some time to do it's job, so I was thinking on delaying the power off for 2 hours but It's not ok to power off slowly decreasing the voltage. Any ideas? Thank you! |
| Wimberleytech:
--- Quote from: paulhm81 on May 31, 2018, 05:12:17 pm ---Hello I'm trying to figure out if there is a way to use the schematic in the picture to cut power but not gradually. I would like to avoid using a relay because they are big and my load will be small (0.2amps) and I would also like to avoid microcontrolers or timers. In my car I have an ionizer and my cigarette lighter is always powered. I thought about changing it to work on contact but the ionizer needs some time to do it's job, so I was thinking on delaying the power off for 2 hours but It's not ok to power off slowly decreasing the voltage. Any ideas? Thank you! --- End quote --- How many components are allowed for your minimalist solution? How much area is allowed? The circuit you have will not work according to your needs, which I think you already know. |
| schmitt trigger:
If you don't want to use a microcontroller, then: The way to go is to use a low frequency oscillator, followed by a divider string. A 2.27Hz oscillator followed by a 14 stage divider would do the 2 hour trick. This can be done with a single CD4060 IC. |
| paulhm81:
I'm only concerned about the size and I'm not that into microcontrolers. I was thinking there is a solution that I'm not aware about like using an additional transistor or a zenner or something. The simplest way I can think of is using a 555. |
| Zero999:
I recently posted a circuit in another thread which does this. https://www.eevblog.com/forum/beginners/a-one-time-timer/msg1574389/#msg1574389 However, in practise a simple RC timer is unsuitable for even a 5 minute delay, let alone 2 hours. The only sane way is with an oscillator and counter, such as the CD4060 mentioned above or a proper time IC such as the MC1/CD4536B or MC1/CD4541B. https://www.onsemi.com/pub/Collateral/MC14536B-D.PDF https://www.onsemi.com/pub/Collateral/MC14541B-D.PDF |
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