Op -Amp.
An operational amplifier, often referred as an op-amp, is a very high gain performance amplifier designed to amplify ac and dc voltage voltages. Modern IC technology and large scale production techniques have brought down the prices of such amplify within reach of all amateurs, experimenters and hobbyists. The op-amp is now used as a basic gain element, like an elegant transistor, in electronic circuits.
A symbol used to represent an op-amp in schematics is shown. The op-amp has two inputs and only one output. One input is called the inverting input and is denoted by a minus sign. A signal applied to this input appears as an amplified but phase inverted signal. The second input is called a non-inverting input and is denoted by a plus sign. A signal applied to this input appears at the output as an amplified signal which has the same phase as that of the input signal.
The availability of two input terminals simplifies feedback circuitry and makes the op – amp a highly versatile device. If a feedback is applied from the output to the inverting input terminal, the result is a negative feedback which gives a stable amplifier with precisely controlled gain characteristics. On the other hand, if the feedback is applied to the non-inverting input, the result is positive feedback which gives oscillators and multi vibrators. Special effects are obtained by combination of both types of feedbacks.
uA741.
Of the different types of op – amps produced, type 741 has achieved a very wide popularity. It is available in 14- pin dual-in line, 8 – pin dual-in line or in TO- style packages.Integrated circuit type 747 accommodates two type 741 operational amplifiers in a single package.
The op-amp needs a dual symmetrical power supply. With its center tap grounded. This enables the op-amp to amplify dc signals of both polarities, positive or negative, with respect to ground. The circuit is so designed that if both inputs are connected to ground, the dc output voltage is zero. However, because of small internal unbalances, a small dc voltage may appear at the output. It is too small to be objectionable in normal applications. For critical applications, the output voltage can be set precisely to zero by connecting a 10K potentiometer between terminals marked “offset-null”.
It is possible to operate the 741 on a single rail supply also. This is usually done by raising the standing dc input voltage to the non-inverting input terminal to approximately half the supply voltage by a voltage divider network. The output dc voltage in such cases stands at half the supply voltage. Bt this does not matter because the dc can be easily blocked by a capacitor allowing only the ac signal to be passed on to the next stage.
The operational amplifier type 741 has many features that have made it so popular. It has an in-built circuitry that provides full protection against output overloads or even shorts to ground for any length of time. The 741 does not need any external component for phase compensation or adjusting its frequency response. This simplifies its circuit design and minimizes the number of components used. Its frequency response has a smooth roll off at the high end which keeps the circuit fully stable in all feedback configurations.
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uA 741 Various package styles .
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uA 741 Pin assignment.
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uA 741 Absolute maximum ratings.
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