LM311 is a general-purpose integrated comparator with low open-loop gain, large offset voltage, and low common-mode rejection ratio however, it has a fast response speed, short transmission delay time, and can directly input high-level signals to the microcontroller. The voltage comparator can convert the analog signal into a binary signal. Therefore, we can use the sensor and potentiometer 1R to convert the gas concentration is converted into a voltage signal and input to terminal 2 of LM311 (that is, V=kC*1R). Since the sensor output current is proportional to the indoor gas (smoke) concentration, that is: The terminal 3 of the integrated voltage comparator LM311 has a constant input of 5V. It is necessary to connect a resistor between pin 7 and pin 8 of the positive power supply, such as about 1kΩ, so that the collector is no longer open. Therefore, when the high level should be output, the high level will not be obtained. Its role is to meet some special needs, such as driving LEDs, lights, relays, and level compatibility with the following digital circuits. The 7th pin among them is the output, which is an open collector structure, that is, the so-called open collector gate, or OC gate for short. The voltage comparator LM311 has 8 pins in total. The pull-up resistor at the output end and pin 1 should be connected to ground.If you want to make a zero-crossing comparator, the 3 pin is directly grounded.Sliding rheostat to divide the voltage, and the maximum resistance can be selected.The basic circuit diagram based on the LM311 design above has the following features and precautions: These circuits have the characteristics of simple structure and low manufacturing cost, which makes the LM311 well used in the circuit.įigure 1. This blog uses take the advantage of the LM311 to introduce and analyze a series of circuits that using the LM311 such as light control and water leak detection. The LM311 is cost-effective, and this is the reason why it is widely used in various comparison circuits. LM311 is a commonly used linear comparator.
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