Basic Question of Op-Amp

Discussion in 'General Electronics Chat' started by Varunblades, Jan 27, 2013.

  1. Varunblades

    Thread Starter New Member

    Feb 11, 2012
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    I am quite enthralled by this forum and would like to say that it's doing a fantastic job at it. Notwithstanding that, I must say that I am a noob at the moment and would greatly appreciate you people's help. My questions would seem silly and sometimes ridiculous, but I am trying very hard, sirs and mams..... trust me.....please be patient and help me with my doubts and I will not let you down....!!!

    1. In my electronics lab, we were given the operational amplifier

    uA 741 CN
    K27052

    It is a DIP8
    What does uA and CN stand for in that name? And what does K27052 stand for?
    (If uA stands for micro-ampere, then why so?)

    2. This question has bugged me since my very first semester:
    If I touch a DC power supply of +10 voltage, both the +ve and -ve wires with my fingers on the breadboard, why don't I feel any current?

    ThankYou ...
     
  2. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Welcome to the forum!

    The ua prefix frequently referred to the particular mfr.

    The CN suffix refers to a package type, or a variant of the IC. Google the ua 741 datasheet for examples.

    The 2nd number is frequently a date code or mfr code.

    Question 2:
    First, Don't ever do this with a much higher voltage. ;);)

    Try this. Set your DMM to the highest ohm setting and check the resistance of your fingers.
    Then, can you figure out why you don't feel much/any current ?
     
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  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The markings on ICs are typically manufacturer and chip type on top line, date code and lot number on second line.

    Reason you don't feel a tingle with ±10V is that roughly 50V (dry skin, 50% humidity) is needed to overcome skin resistance. If you are sweating, the resistance lowers, such as when working on a car battery in shorts, leaning bare legs against bare metal on the car, then touching the +12V Terminal gives a tingle. Similar to licking a 9v battery for testing if 9v is good or not, but over a bigger area with car battery, though not very dangerous.

    Generally, circuits under 50V cannot "push" enough current to be dangerous. Above that, it goes from being felt to lethal quickly with rising voltage, though very dependent on path. Electricity passing chest/head it is worse than if it jumps from finger to palm, for example. Electricity flow between two arms is a good way to mess up heart timing, hence the "one hand in your pocket" rule when working on higher voltage circuits. These safety reasons are why those circuits are not open for discussion on this forum.
     
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  4. crutschow

    Expert

    Mar 14, 2008
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    I believe the μA in front of the 741 stood for "micro amplifier". The device was built in the early days of integrated circuits (being the first internally compensated IC op amp) and they wanted to emphasize that it was a small integrated circuit amplifier.
     
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  5. Audioguru

    New Member

    Dec 20, 2007
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    The very old 741 is a lousy opamp. There are much newer, better opamps that cost the same.
     
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  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    uA is the prefix originally used by fairchild many decades back.

    C is the temp range (C for commercial which is usually -40 to 125C junction temp) and the N is the package type which is probably a plastic DIP.

    my guess is "27" is the work week of the year and "05" is the year of manufacture. The last number could be a manufacture location code?
     
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  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    But all schools have bags of 741's left over that they give students to blow up.
     
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  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Audioguru, do you have this phrase assigned to a hot key combination on your keyboard?:D
     
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  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    He might, but people should be aware of that fact. Since radio shack sells the 741 for a few dollars, people unhappy with the performance or want to use a single supply think one that is better would cost $10 or more.

    He should put his message in his sigline.
     
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  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Yeah, I think Audioguru is doing the noobs a service by pointing out the 741's shortcomings.
     
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  11. MrChips

    Moderator

    Oct 2, 2009
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    uA is Fairchild's label, the manufacturer. C is the temperature range and N is the package (as already reported by bountyhunter).

    My guess is 7052 is the manufacturing date stamp, week 52 of 1970.
     
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  12. Varunblades

    Thread Starter New Member

    Feb 11, 2012
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    Thank You for the warm welcome tubeguy. :)

    I searched what 'mfr' stood for. Is it 'multi frequency receiver'? I went to its wikipedia page but couldn't relate much. Could you explain it in detail? *fingers crossed*

    Question 2: Yeah, I found that the resistance provided by our body is in the range of mega ohms (I read this while researching on 'ABCs of multimeter safety' by FLUKE. I had also tried it with my DMM in my lab). Hence, as pointed out by thatoneguy, I get it why we don't feel the zing.

    Thank You so much for it.
     
  13. Varunblades

    Thread Starter New Member

    Feb 11, 2012
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    Thank You so much ...
    But why did they come up with something like uA as if calling out micro-ampere or micro-amplifier (pointed out by crutschow)?
    I know that instead of concentrating on more important things like the workings/applications of 741, I am indulgin in such trivial things but you guys are the best in the world...you people must be knowing everything....:)
     
  14. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Robert Noyce, the founder of Fairchild Semiconductor, gave marketing the choice of calling it the uA741 or the Noyce741.
    Marketing feared that some might mispronounce Noyce, thinking it was the Noisy741. They chose uA741, and the rest is history.
     
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  15. MrChips

    Moderator

    Oct 2, 2009
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    Yet, it did end up being Noisy741, according to audioguru.
     
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  16. Audioguru

    New Member

    Dec 20, 2007
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    If you like bacon frying sounds then use a lousy old 741 opamp "HISSSSSSSSS" in an audio circuit. Also its slew rate is so slow that it misses producing the top octave of sounds.
    Deaf teachers do not care.

    EDIT: The same for the lousy old LM324 and LM358 horrible opamps. They have the bonus of crossover distortion.
     
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