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TLDR : Ideal supply voltage of a device is 12v DC (labeled near jack). User may mistakenly provide anything from 3 to 24 DC (or maybe 220v AC). how to protect the circuit against Over-Voltage ? how to turn off all the circuit (at least mCU) in case of Under-Voltage (less than 12v)?

I'm trying to come up with a protection on the power supply of a circuit. the input voltage is supposed to be 12v DC. (which will be provided by the product end user through a 5mm power jack). An internal regulator provides 5v for Microchips and other ICs, also the input 12v is needed for some other components.

the whole device should be protected against OV if mistakenly a voltage higher than the required 12v is provided. (eg. 24v DC, or even 220v AC from mains).

these are all the OV protection methods I know so far. which one is a better choice? :

  • A few Zeners (with different Vz ratings) cascaded to regulate the input voltage in few steps.
  • Zener + Darlington BJTs
  • Common DC-DC buck converter ICs
  • Crowbar
  • Varistors
  • Two NPN transistors in common base (regulates to Max EB voltage)
  • Zener + Fuse combo

and for Under-Voltage protection I have no idea. (mCU off if supplied V < 12v)

Circuit Power Diagram

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    \$\begingroup\$ You have three problems that need three solutions. Treat each one separately. \$\endgroup\$
    – Kartman
    Commented Apr 20, 2021 at 21:54
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    \$\begingroup\$ 12 to 24v overvoltage can be done with zener+transistors just by disconnecting high side leg if overvoltage (defined with zener) apears. The undervoltage is a bit harder, you must think about many situation can happened, how fast it must to be, what critical task you doing in MCU, how regulators behave during undervoltage. If you supply MCU with separate big capacitor you have enough time just by sensing 12v bus with ADC to save critical data/writing eeprom etc... \$\endgroup\$
    – user208862
    Commented Apr 21, 2021 at 0:14
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    \$\begingroup\$ Well, the first problem is the specs. You must regulate out a 12 V when given a 12 V source. That'll be interesting to do with 0 V overhead to work with. Also, you've no specifications about current compliance. Without knowing what could happen, wouldn't it be difficult to arbitrarily just say "crossbar is better?" It would be so nice if a simple block diagram like yours is all that anyone would ever need to analyze and that the answer for it would apply in all situations it appears to cover. Wouldn't even need a design engineer, then. Just apply bright-line rules and crank out result. \$\endgroup\$
    – jonk
    Commented Apr 21, 2021 at 0:15

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