Comparator latch circuit

Question

I need a VERY simple latching circuit using a comparator that will simply be off until a signal hits it (can be either + or -, I have no preference). The circuit should remain on until I reset it.

Answer 1

You could do something like this- the comparator output goes low when the input passes +2.50VDC (the voltage set by the R3/R3 resistor divider, which turns on the LED D1 and also Q1. Q1 pulls the inverting input up to +5 regardless of the voltage at the input so the LED will not turn off. SW1 shorts out the transistor drive so the LED will turn off and, if the input voltage is less than 2.5V, will stay off when the switch is released. Otherwise it will come on again immediately when the switch is released.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

With a comparator and a D-flipflop (74hc74) use the output of the comparator (with a pull-up resitor) as flipflop CLK. Set the flipflop D=1, S=1, and use R as reset. The output of the flipflop Q is the Latched output.

Answer 3

with a bit of positive feedback it's easy to make a comparitor latch.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 4

^{simulate this circuit – Schematic created using CircuitLab}

My first schematics, just as example

Answer 5

Open drain comparator with Vtrip = 2.5V. When comparator negative input is above 2.5V, comparator outputs low, diode conducts and Vtrip becomes ~0.7V. Comparator output stays low (or latched).