Op-Amps 1: Description

by gaussmarkov

Appearance

LM741 ICOp-amps (operational amplifiers) come in an integrated circuit, or IC. The one pictured on the right is in a form called DIP-8, which is short for dual in-line package with 8 pins. “Dual in-line” refers to two lines of pins, in this case 4 on each side. Each pin has a special function and they are numbered from 1 to 8. Often, there is a circle on the top of the case to show the location of pin 1. Also the case is usually notched at the same end with half-circle cut-out. At least one of these two markings appear, but not necessarily both.

The manufacturer, its documentation, and the name of the chip are printed on the top. In this case, the leading symbol is the circular N logo of National Semiconductor and the name of the chip is LM741CN. The DOD Overdrive 250 and the MXR Distortion Plus are popular examples of stompboxes built around this chip.

The names of chips are often abbreviated to their numbers, like 741. Different manufacturers may use different prefixes and suffixes while keeping the same numbers. For example, JRC produces the NJM741D. Although generally they can be used as functional substitutes, chips with the same numbers but different names are not necessarily identical. One of the characteristics that is often flagged with the suffix is the package or case of the IC. For example, National Semiconductor also manufactures the LM741H which is the 741 in an 8-pin “metal can.”

DIP-8 Pinout DiagramThe numbering of the pins is always the same. With the notch or pin 1 marking at the top, count sequentially from pin 1 down the left side and then up the right side of the DIP. In other words, count counter-clockwise (CCW).

Op-amps can be soldered directly to the circuit board but often op-amps are seated in sockets instead. The sockets are soldered to the board, avoiding the risks of destroying the op-amp with too much heat. Also, one can exchange op-amps easily to make a repair or to try an experiment (like on a breadboard). A DIP-8 machine-pin socket by Mill-Max and a DIP-8 dual-leaf socket by AMP are shown below.

Dual-Leaf DIP-8 socketMachine-pin DIP-8 socket

These sockets also have notches like the op-amps so that even without the op-amp on the board its orientation is still clear.

Symbols

Basic op-amps are denoted on schematics by a simple triangle that usually points to the right.

Op amp schematic symbol

They have two inputs on the left-hand side, denoted by positive and negative signs, and a single output at the point on the right. The inputs are often shown in the opposite order.

Above and below are power supply connections, with the positive supply above and the negative supply below.

These directions are associated with typical audio schematic layouts, where the input is on the left, the output is on the right, the positive power connections go up, and negative or ground connections go down. Often, when they are implicitly clear, the power connections are not shown (as on the right).

Op amp layout symbol On circuit board layouts, one sees the outline of the IC package. The characteristic notch appears at the end where pin 1 is located. On gaussmarkov.net layouts, the pad for pin 1 is also square while all of the other pads are round.

Values

Op-amps do not have a single salient characteristic like resistors and capacitors do. Op-amps are designed with various special tasks in mind so that they are particularly good in specific ways. The design goals include gain, low noise, fast response, high input impedance, and low output impedance.

741 pinoutDIP-8 op-amp ICs may contain one or two op-amps. The 741 contains only one op-amp. The 4558 that is found in tubescreamers has two and is often called a dual op-amp. You will also run into quad op-amps that contain 4 op-amps in a DIP-14 package. The pin assignments (or pinout) for the 741 can be described by drawing the op-amp into a pin diagram
so that the two inputs are connected to pins 2 and 3, the output is connected to pin 6, the positive power supply to pin 7, and the negative power supply to pin 4. Pin 8 serves no purpose. We will discuss pins 1 and 5 in a later note.

DIP-8 Dual Op Amp PinoutDual op-amps like the 4558 generally have the same pinouts so that their ICs can be interchanged in circuits that use them with sockets. This is a popular thing to try with stompboxes like the tubescreamer. Op-amp A has inputs on pins 2 and 3 and output on pin 1 on one side while op-amp B has inputs on pin 5 and 6 and output on pin 7 on the other side. The positive and negative power pins are 8 and 4, respectively. On a schematic these op-amps would be labeled IC1A and and IC1B and the power supply pins for one would serve both.


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13 Responses to “Op-Amps 1: Description”

  1. Electronics-Lab.com Blog » Blog Archive » [Basic Electronics] – Op-Amps Tutorial said:

    […] Op-Amps 1: Description […]

    Posted 01.02.2008 at 1:55 am

  2. Anonymous said:

    ty

    Posted 27.05.2008 at 10:58 pm

  3. Sander de Groot (Asfastasdark) said:

    Of the two DIP-8 sockets listed above, which do you prefer, and why, and also, how do they hold the op-amp in place? Are the socket holes wedge shaped, so they clamp the pins when you push them down?

    Posted 06.09.2008 at 6:24 pm

  4. LiViNG^TeaRs said:

    Thx you much.. i searched and found the right thing… i hope i make it right 😉 (sry.. but my english is bad =( )

    Posted 11.02.2009 at 10:06 pm

  5. Glen said:

    Thanks
    For providing this info.
    It will go to good use.

    Glen

    Posted 21.04.2009 at 7:40 pm

  6. Amit said:

    plz tell me what is the actual purpose of pin 1,5 & 8 in the op amp 741 ic which contains only one Op-Amp?

    Posted 10.09.2009 at 11:13 pm

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    Posted 10.02.2010 at 12:07 am

  8. SATYARANJAN SWAIN said:

    where is the function of pins?

    Posted 17.02.2010 at 3:33 am

  9. pramida said:

    plzzz tell me what does 741 mean and all explain me all the writings on the op amp

    Posted 03.05.2010 at 9:33 pm

  10. Anonymous said:

    Splendid

    Posted 24.05.2010 at 1:37 pm

  11. Maze said:

    It is wonderful

    Posted 24.05.2010 at 1:56 pm

  12. Joe Gavin said:

    Gauss, excellent sharing!!

    To others who ask for pin details, please please view the data sheet, details are there. Writings on the opamp usually carry the date code among other things.

    Posted 27.09.2010 at 1:33 am

  13. Theophilus said:

    Pls, help me to fix the name and functions of the pins. Because l can’t really get it from the explaination.

    Posted 24.06.2012 at 6:52 am