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Op Amp Function
In analog circuits, signals frequently need "boosting" to make up for weak signals and energy losses in components. An op faithfully reproduces a signal while increasing its voltage. By carefully choosing the resistors used with the op amp, it can increase signals by over a thousandfold. It can also add and subtract signals and combine alternating current, or AC signals with direct current, or DC. It can handle a range of input signals, from microvolts to 30 volts.
Supply Voltage
A circuit using an op supplies it with a fixed, well-regulated voltage to power the device. Some op amps, such as National Semiconductor's LM741, need a bipolar power supply, meaning it supplies positive and negative voltages, plus ground. Other models, like the LM358, can run on a positive voltage and ground. The op amp's supply voltage, unlike its input voltage, must have a fixed value. Because the output depends on both the input and the supply voltage, the supply must be as free as possible from electrical noise and unwanted variations.
Input Voltage
The op amp's input voltage comes from another device or circuit; the voltage needs amplifying or processing in some fashion. It can be steady DC, varying DC or AC. If the input is a signal with a frequency, an op characteristic called the gain-bandwidth product set limits as to how high a frequency it can process; an op can amplify more but at a cost of more restricted high frequencies. The op has two inputs, one that inverts and one that does not. The inverting input, designated by a minus sign, "flips" the sign of the voltage before amplifying it. For example, a 1-volt signal becomes negative 1 volts at the output, while negative 1 volts becomes 1 volt. The non-inverting input simply passes the voltage as-is before amplifying it.
Clipping
An electronic designer using an op in a circuit must take care that the maximum input voltage remains significantly less than the supply voltage. The op amp's output cannot be greater than the supply voltage. For example, an op with a gain factor of 10, having an input voltage of 2 and a supply voltage of 10 volts, cannot output 20 volts, but instead will output something close to 10 volts. On the other hand, an op with a gain of 10, an input of 1 volt and a supply of 20 volts will produce 10 volts at its output, since plenty of "headroom" remains between 10 and 20 volts. If the input times the gain exceeds the supply voltage, the op does what it can but "chops off" the peak voltages and produces a distortion called "clipping."
Voltage Limits
Every op has limits on how much voltage its supply and input connections can handle. The op amp's data sheet specifies these and other figures in a section called "Absolute Maximum Ratings." If the circuit exceeds these limits, it may destroy the device.