Comparator input below V-

Question

I am searching for a way to use a comparator with possible negative voltage on its inputs.

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My thoughts and attempts so far:

• Op amps and comparators with V+, V- and GND: the circuit utilizes a single LiPo battery.
• LM339/393: works correctly only when Vin >= V- - 0.3V, which is not enough.
• Diodes: too low voltage, I suppose

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Requirements are:

• Vin range -2.0V .. + 2.0V (and around 0.1V on the reference)
• Max. current provided for comparator input: around 500 uA

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Recently I have found an interesting comparator - LT1716 (datasheet/website). It provides a "Valid Output with Either Input 5V Below V– ". If there is one, then the idea is not new and there should be more, right?

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(I am new to electronics, and I am sorry if I did not provide some related info - please let me know what I forgot)

Answer 1

This may give you some ideas:

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Comparitor to handle negative voltages.

• R3 sets a threshold between 0 and V+. If this is too coarse add series resistors at the top and/or bottom of the pot to narrow the range of adjustment for easier adjustment.
• The trick of the circuit is to feed the non-inverting input from a potential divider, the top of which is connected to V+. In this example \$ V_A = V_+ - \frac {V_+ - V_{IN}}{2} \$ so the input voltage can range from \$ \pm V_+\$