Toggle the SPDT switch to change the input voltage. Push the push button to reset the latch. The circuit doesn't unlatch until the input voltage is below the trip voltage.
This is an over-voltage protection circuit that locks-out and latches when the input exceeds 10V. The lockout voltage is set by the resistor divider. The output of the divider is set to a comparator with a threshold voltage of 2.5V (TL431 can be used for this). The lockout voltage is given by
V(ovlo) = 2.5(1+R2/R1).
The output of the comparator is fed to a latch, which can be reset by pushing the push button. The latch shuts the PMOS off, thus protecting the load from an over-voltage.
Previous circuit: http://everycircuit.com/circuit/5189504508624896
Advantages of this circuit over my previous circuit:
-Uses an op amp to set the lockout voltage; therefore, it is very precise.
-Has a latching feature due to which any fluctuations in the input voltage around the lockout voltage cannot make the circuit keep turning off and on.
Disadvantages:
-More complex.
-The maximum input voltage is limited by the maximum power supply voltage of the op amp (usually around 30V). In my previous circuit, the max input voltage is limited by the Vds(br) of the MOSFET.
The reason why I haven't presented this circuit with a Vout - Vin type graph with an input triangle waveform is because this is a latching type circuit. As soon as the input exceeds the trip voltage, the circuit latches off and the output permanently goes off. The output would be 0 for any input voltage, even when it goes under the trip voltage.
