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I am currently trying to come up with an analog timing circuit to use within a solar tracker. I know using a 555 timer would be relatively easy to do here but I wanted to see if I could come up with a different way to do this. I'm new to designing my own circuits and was wondering if the following circuit has any major flaws that I'm overlooking.

I was hoping to trigger a different part of the circuit by slowly charging the capacitor up until the threshold voltage for the MOSFET was reached (the source will be tied to ground with a pull down resistor). The resistor and capacitor values will be chosen so that the threshold would be met about every 15 minuntes. After this point, the MOSFET would provide power to the rest of the circuit. As the capacitor continues to charge, it would eventually reach the threshold voltage for the DIAC. This would occur roughly 1 minute after the MOSFET started conducting. The DIAC would then start conducting and the capacitor would be discharged to ground, turning off the MOSFET and starting the cycle over again.

Since I'm new to think kind of thing I was just hoping for some guidance to see if this thinking is correct. I haven't really come across this use case for a DIAC anywhere else and kind of assume I'm overlooking something if that is the case. Thanks in advance!

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pointy
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  • Your circuit seems a bit strange to me. First of all, the MOSFET threshold voltage is defined between gate and source. I don't see where your source is heading to, so this is kind of undefined in this schematic. Please explain what your circuit needs to do, maybe with a timing diagram. – Stefan Wyss Apr 20 '23 at 06:02
  • Generally, DIAC are used with SCR or TRIAC ... Not with MOSFET. – Antonio51 Apr 20 '23 at 07:08
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    What diac are you proposing? The ones I found had break over voltages around 30V which clearly won’t work for you with a 15V supply. As well, power mosfets may not appreciate being fed with a slow voltage ramp as this may cause overheating or failure. Something like a NE555 might be a more valid solution. – Kartman Apr 20 '23 at 13:17

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