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Voltage comparator


This experiment only requires a single operational amplifier. The model 1458 and 353 are both “dual” op-amp units, with two complete amplifier circuits housed in the same 8-pin DIP package. I recommend that you purchase and use “dual” op-amps over “single” op-amps even if a project only requires one, because they are more versatile (the same op-amp unit can function in projects requiring only one amplifier as well as in projects requiring two). In the interest of purchasing and stocking the least number of components for your home laboratory, this makes sense.

LEARNING OBJECTIVES

SCHEMATIC DIAGRAM

ILLUSTRATION

INSTRUCTIONS

A comparator circuit compares two voltage signals and determines which one is greater. The result of this comparison is indicated by the output voltage: if the op-amp’s output is saturated in the positive direction, the noninverting input (+) is a greater, or more positive, voltage than the inverting input (-), all voltages measured with respect to ground. If the op-amp’s voltage is near the negative supply voltage (in this case, 0 volts, or ground potental), it means the inverting input (-) has a greater voltage applied to it than the noninverting input (+).

This behavior is much easier understood by experimenting with a comparator circuit than it is by reading someone’s verbal description of it. In this experiment, two potentiometers supply variable voltages to be compared by the op-amp. The output status of the op-amp is indicated visually by the LED. By adjusting the two potentiometers and observing the LED, one can easily comprehend the function of a comparator circuit.

For greater insight into this circuit’s operation, you might want to connect a pair of voltmeters to the op-amp input terminals (both voltmeters referenced to ground) so that both input voltages may be numerically compared with each other, these meter indications compared to the LED status:

Comparator circuits are widely used to compare physical measurements, provided those physical variables can be translated into voltage signals. For instance, if a small generator were attached to an anemometer wheel to produce a voltage proportional to wind speed, that wind speed signal could be compared with a “set-point” voltage and compared by an op-amp to drive a high wind speed alarm:





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  1. Guru

    A dedicated voltage comparator will generally be faster than a general-purpose operational amplifier pressed into service as a comparator. A …
    If there is a fixed voltage source from, for example, a DC adjustable device in the signal path, a comparator is just the equivalent …
    When the voltages are nearly equal, the output voltage will not fall into one of the logic levels, thus analog signals will enter …
    http://en.wikipedia.org/wiki/Comparator

    Voltage Comparators
    This page provides basic information about voltage comparator integrated circuits and is to act as reference material for other circuits. The …
    The LM311 Voltage Comparator can be used for these applications as well and also has a number of unique features. …
    An integrated circuit “Voltage Comparator” is equivalent to an Operational Amplifier, Such as the LM358 or LM324, with two NPN transistors added to the output of each amplifier. ( …
    http://home.cogeco.ca/~rpaisley4/Comparators.html

    LM311 – Voltage Comparator
    The LM111, LM211 and LM311 are voltage comparators that have input currents nearly a thousand times lower than devices like the LM106 or LM710. They are also designed to operate over a wider …
    Temperature Min, 0 deg C, -40 deg C, -40 deg C. Temperature Max, 70 deg C, 125 deg C, 85 deg C. Function, Comparator, Comparator, Comparator …
    AN-1378: Application Note 1378 Method For Calculating Output Voltage Tolerances in Adjustable Regulators, 647 …
    http://www.national.com/pf/LM/LM311.html

    Voltage Comparator. 1.0 General Description. The LM111, LM211 and LM311 are voltage comparators that. have input currents nearly a thousand times lower than …
    negative supply voltage or 30V below the positive supply, whichever is less. Note 5: The maximum junction temperature of the LM111 is 150˚C, while …
    temperature specifications are limited to −25˚C≤TA≤+85˚C. The offset voltage, offset current and bias current specifications apply for any supply …
    http://www.national.com/ds/LM/LM111.pdf

    ALD Precision CMOS Voltage Comparators Pre-Amp and Output Driver
    A family of precision voltage comparators are available as micropower devices with very low input currents and high output current drivers. Again …
    http://www.aldinc.com/ald_vcomp.htm

    LM2903. Low power dual voltage comparator. Features. ■ Wide single supply voltage range or dual. supplies +2 V to +36 V or ±1 V to ±18 V …
    power voltage comparators designed specifically. to operate from a single supply over a wide range. of voltages. Operation from split power supplies is. also possible. …
    common-mode range, the comparator will provide a proper output state. The low input voltage state must not be less than …
    http://www.st.com/stonline/books/pdf/docs/2470.pdf

    Linear Technology – LT1011/LT1011A – Voltage Comparator
    Although pin compatible with the LM111, it offers four times lower bias current, six times lower offset voltage and five times higher voltage gain. Offset voltage drift, a previously unspecified parameter, is guaranteed at 15µV/°C. Additionally, the supply current is lower by a factor of two …
    LT1011/LT1011A – Voltage Comparator. Features; Description; Packaging; Order Info; Simulate; Print Friendly …
    http://www.linear.com