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I want to build an over voltage protection with adjustable voltage limiter. Operation range would be 5-12 volts. The protector would be "self recovery" - it will reset if voltage again goes under that set by Variable Resistor.

Since this will be operate on high current, using relay is preferred.

basically it's just a relay activator that will operate on certain voltage. i.e : Scenario: i want to limit my work at 5 volts max. So the relay will be switched on if voltage is > 5 volts, (set by VR), and again in will be switched off if voltage goes under 5 volts.

This also will protect the worst case emitor-collector leak (i am using linear voltage regulator).

I am thinking about resistors, zener and bipolar transistors. How is the design would be ?

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  • \$\begingroup\$ There is an inherent danger with this type of design. If the input voltage fluctuates, it can switch the relay on and off rather quickly, and that is usually a bad thing. May cause either the relay or the attached load to fail. The part of the circuit that disconnects the relay can be analog, and fast-acting, but the part that turns it back on should probably be digital, and should only turn it back on after a few seconds. \$\endgroup\$ – mkeith Nov 6 '16 at 17:14
  • \$\begingroup\$ stop thinking relay, zener etc and "implementation specific" ideas and restart think of all IO specs for V,I,Pd,t, f domain and thermal environment range, max hotspot, then add Zin,Zout(f,t) with tolerances as much as possible on everything then write a point form datasheet or Requirements Statement or a "Spec". Do the same for anything including Coding. look up IBM's Hierarchical InPut Output documentation for ideas. Aka HIPO. This is conceptually how good designers think and by avoidance how companies fail.. including IBM on some outsourced projects \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 6 '16 at 17:14
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OVP, OCP, OTP, UVP, etc is usually done with very low ESR series controlled switches with transient reverse protection. (external) Make Rdson<2% of DC resistance or V drop at peak current for efficiency. If a Relay or Contactor for really high power is cheaper, consider MTBF ratings with DC and inductive loads with ratings.

Hiccup recovery requires I*t sensing and safe wait times for cool down or short circuit sensing from RdsOn/Rload voltage ratio with a pulse test.

LDO's use OTP ( with buried diode voltage) and OCP (with ~50mV current shunt) and have emitter follower outputs for 1~2V dropout or common drain series outputs for xx or xxx mV dropouts.

%Step Load V Regulation= ESR source/ step load Z ...impedance ratio

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