Sunday, 3 March 2019

operational amplifier - "Standard" components...?


In class we are designing a few different circuits and it uses some diodes and opamps. Everything is fine on paper and everything makes sense. These are only ever refereed to as a "diode" or "opamp".


So then I made a simulation on pspice. However depending on what diode or opamp I choose the results I got were completely different. There where many opamps and diodes to choose from in the component list.


Until now I just thought a diode is a diode or opamp is an opamp as there's never been any more specifics on them. Nothing like a resistor or capacitor where you have to choose the correct value component to get it all to work.


So I was wondering when people say "use an opamp" is there a standard common / specific opamp that is the general one used.


Same with the diodes. Is there a standard go to diode that is used in all circumstances ..unless otherwise stated.



After thinking about it..what about transistors also?



Answer



Here are the types I immediately think of when someone says "diode", "op-amp", ...



  • Op-amp : LM741. The first "easy to use" op-amp IC on the market.

  • Diode : 1N4001. General purpose silicon diode good up to 50V blocking voltage and 1 amp current. The 1N4002, 1N4003, etc. are similar diodes with higher voltage ratings.

  • Transistor: 2N2222. NPN bipolar junction transistor. The 2N2907 is apparently the PNP equivalent.

  • (Linear) Voltage regulator : LM78xx series, i.e. the LM7805 for 5 V, the LM7812 for 12 V.

  • Digital logic, i.e. NAND gates and so on: 7400 series and 4000 series.



These are extremely common, basic parts. If you walked into a hobby store and asked for a hundred transistors, without specifying anything else, you would probably get a bag of 2N2222's.


This is not to say these parts are useful for everything - they have limitations on voltage, current, speed, accuracy, and so forth. But if you have to pick a type of component for the purposes of a SPICE simulation, these will work fine.




Edit: For reference, here are the "default parts" you get in CircuitLab:



  • Op-amp TL081

  • Diode 1N4148

  • Zener diode 1N4733A

  • NPN BJT 2N3904

  • PNP BJT 2N3906


  • N-channel MOSFET IRF530

  • P-channel MOSFET IRF9530

  • N-channel JFET J310

  • P-channel JFET J271


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