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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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