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Operational Amplifiers - 741 (1)

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  • Nicolae Sfetcu
    What Exactly Is An Op-Amp? What exactly is an OPerational AMPlifier? Let s define what that component is and look at the parameters of this amazing device. The
    Message 1 of 1 , Jun 18, 2001
      What Exactly Is An Op-Amp?

           What exactly is an OPerational AMPlifier? Let's define what that component is and look at the parameters of this amazing device.
      The term 'op-amp' was originally used to describe a chain of high performance dc amplifiers that was used as a basis for the analog type computers of long ago. The very high gain op-amp IC's our days uses external feedback networks to control responses. The op-amp without any external devices is called 'open-loop' mode, refering actually to the so-called 'ideal' operational amplifier with infinite open-loop gain, input resistance, bandwidth and a zero output resistance.
      However, in practice no op-amp can meet these ideal characteristics. And as you will see, a little later on, there is no such thing as an ideal op-amp. Since the LM741/NE741/µA741 Op-Amp is the most popular one, this tutorial is direct associated with this particular type. Nowadays the 741 is a frequency compensated device.

      Let's go back in time a bit and see how this device was developed.
      The term "operational amplifier" goes all the way back to about 1943 where this name was mentioned in a paper written by John R. Ragazzinni with the title "Analysis of Problems in Dynamics" and also covered the work of technical aid George A. Philbrick. The paper, which was defined to the work of the U.S. National Defense Research Council, was published by the IRE in May 1947 and is considered a classic in electronics.
      The very first series of modular solid-state op-amps were introduced by Burr-Brown Research Corporation and G.A. Philbrick Researches Inc. in 1962. The op-amp has been a workhorse of linear systems ever since.
      The first op-amp offered to the public in 1963 was the µA702 manufactured by Fairchild Semiconductors but it had very weird supply voltages such as +12 and -6volts.

      Below in Fig.1 are op-amp symbols as used today. The one on the right is an older way of drawing it but still used in books like the ARRL (American Radio Relay Leaque) and older schematics. It is common practice to omit the power supply connections as they are implied.

      Op-Amp Schematic Symbols

      Absolute Maximum Parameters:
      Maximum means that the op-amp can safely tolerate the maximum ratings as given in the data section of such op-amp without the possibility of destroying it. The µA741 is a high performance operational amplifier with high open loop gain, internal compensation, high common mode range and exceptional temperature stability. The µA741 is short-circuit protected and allows for nulling of the offset voltage. Manufactured by Signetics Corporation.

      µA741 Maximum Ratings
      1. Supply Voltage (- + Vs): The maximum voltage (positive and negative) that can be safely used to feed the op-amp.
      2. Dissipation (Pd): The maximum power the op-amp is able to dissipate, by specified ambient temperature (500mW @ <80° C).
      3. Differential Input Voltage (Vid): This is the maximum voltage that can be applied across the + and - inputs.
      4. Input Voltage (Vicm): The maximum input voltage that can be simultaneously applied between both input and ground also referred to as the common-mode voltage. In general, the maximum voltage is equal to the supply voltage.
      5. Operating Temperature (Ta): This is the ambient temperature range for which the op-amp will operate within the manufacutre's specifications. Note that the military grade version (µA741)has a wider temperature range than the commercial, or hobbyist, grade version (µA741C).
      6. Output Short-Circuit Duration: This is the amount of time that an op-amp's ouput can be short-circuited to either supply voltage.
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