Operational Amplifiers

The temperature detector fire alarm system consists of a thermistor sensor whose resistance changes in case of a fire, altering the signal voltage. This signal change is too small to directly trigger the alarm. So, the signal is processed by an operational amplifier, often called an op-amp, to activate the alarm system.

Op amps are commercially available in a variety of integrated circuit packages. One of the most common is the LM741, sold in an eight-pin dual in-line package.

Typically, an op amp has eight pins: two input pins, one output pin, two power supply pins, two offset-null pins for calibration, and one unused pin.

The circuit symbol for an op amp is a triangle, with the inverting input marked with a minus sign and the non-inverting input with a plus sign.

An op amp, in conjunction with other circuit elements, can also perform a broad range of signal-processing operations.

Additional power supplies are used to bias the operational amplifier. The current drawn from power supplies is the sum of the output current and the current required to power the amplifier internal circuitry.