Dislike my Lab class: semicon. circuits

In summary, the conversation discusses the concepts of circuits, specifically diodes, transistors, and op-amps, and the equations that govern their behavior. The person asking for help has never taken a circuit analysis class before and is struggling to understand the fundamentals. They ask for clarification on the ideal equations for transistors and op-amps, as well as the principle equation for op-amp 741. The expert suggests building a foundation in circuit analysis before attempting to understand these concepts. They also mention the T-approximation for transistors and explain how the gain for a non-inverting op amp circuit is determined.
  • #1
tim_lou
682
1
I'm currently enrolled in a lab class about circuits. we are doing diodes, transistors, op-amps these days.

the thing is, I've never taken any circuit analysis before, but the prof. expects us to be able to understand op-amp, diodes, transistors... and be able to calculate quantities for complicated circuits involving these things.

My question is what equation governs ideal transistor and op-amp?

for instance, for resistor, V=IR.

what about transistors and op-amps? I have searched for many books in the library (they are either too complicated or too simple to include diodes) and struggled with my book (the book is like a layman introduction to circuits... I don't like that style... the math is sketchy and derivations are usually omitted)

I know for ideal transistor, current through emitter = current through collector...is that correct? what about voltage?

and for op-amp... I really don't know.
so for op-amp, what is the governing equations/relations regarding
1. -input
2. +input
3. output
in terms of voltage and current?

I just need to know the fundamental equations about these things... It will be appreciated if anyone can help me... thanks for your reading.
 
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  • #2
Check out a copy of Horowitz and Hill, Art of Electronics for a straightforward no-nonsense presentation of all things electronic.
 
  • #3
I know for ideal transistor, current through emitter = current through collector...is that correct? what about voltage?

You can say that since the base current is very small compared to emitter current. The voltage across base-emitter and base-collector is the same principle as a diode when forward biased and reversed biased. Remember that a diode consist of n-type and p-type material (NP), and a bjt transistor consist of either NPN or PNP.
and for op-amp... I really don't know.
so for op-amp, what is the governing equations/relations regarding
1. -input
2. +input
3. output
in terms of voltage and current?
Its too broad of a question. What kind of op-amp?
 
  • #4
Perhaps you need to step back and enroll into a circuit analysis class that teaches op amps, bjts, and diodes before you take this class.
 
  • #5
Yeah man, that class would be crazy without the necessary foundation. We used Microelectronic Circuits (by Sedra and Smith) in my course, I really liked this book.
 
  • #6
tim_lou said:
I'm currently enrolled in a lab class about circuits. we are doing diodes, transistors, op-amps these days.

the thing is, I've never taken any circuit analysis before,

my question is how do you find yourself in an electronic circuits lab and you've never had a class with KCL, KVL, loop-current, or node-voltage, etc?

but the prof. expects us to be able to understand op-amp, diodes, transistors... and be able to calculate quantities for complicated circuits involving these things.

My question is what equation governs ideal transistor and op-amp?

for instance, for resistor, V=IR.

strictly speaking, i think it's the Ebers-Moll equation for the ideal BJT and op-amps are s'pose to be ideal voltage-controlled voltage sources with low output impedance and high input impedance. but don't deal with the Ebers-Moll eq. instead...

what about transistors and op-amps? I have searched for many books in the library (they are either too complicated or too simple to include diodes) and struggled with my book (the book is like a layman introduction to circuits... I don't like that style... the math is sketchy and derivations are usually omitted)

I know for ideal transistor, current through emitter = current through collector...is that correct? what about voltage?

... deal with the transistor as a current-controlled current source with some output impedance and a pretty low input impedance.

i don't know what the pedagogy is that you're in, but you should have had the fundamentals of circuit analysis before getting to the lab course you're in.
 
  • #7
thx for the replies

ranger said:
Its too broad of a question. What kind of op-amp?

sorry about that. I meant op-amp 741. the book presents a bunch of usages of this thing, including inverting amplifier, non-inverting amplifier, differentiator and integrator... the book never says anything about principle equation... for instance, in the derivation of gain in non-inverting amplifier, the book says that the negative input and positive are at the same voltage (for op-amp 741). I don't know if that is true or not... is it true in general? or??
 
  • #8
rbj said:
my question is how do you find yourself in an electronic circuits lab and you've never had a class with KCL, KVL, loop-current, or node-voltage, etc?

the class is designed for physics majors... it is just a part of the standard computer based lab for physics majors. the prereq. is just some freshman "modern physics" class... anyway.

rbj said:
deal with the transistor as a current-controlled current source with some output impedance and a pretty low input impedance.

so, I think I know what you are talking about... the T approximation or something like that? I think I got that one.

perhaps you can tell me what the op-amp is equivalent to in a circuit? (approximately?)
 
  • #9
tim_lou said:
thx for the replies
sorry about that. I meant op-amp 741. the book presents a bunch of usages of this thing, including inverting amplifier, non-inverting amplifier, differentiator and integrator... the book never says anything about principle equation... for instance, in the derivation of gain in non-inverting amplifier, the book says that the negative input and positive are at the same voltage (for op-amp 741). I don't know if that is true or not... is it true in general? or??
It is the bunch of uses for the op-amp that give rise to the numerous equations. There isn't any principle equation to relate those aspects that you've requested. It just changes from application to application. As for the gain for a non inverting amp, I'm afraid that it isn't the same principle for the other op-amp configurations.

The circuit to the right shows a non-inverting op amp circuit. In this circuit, the input signal is effectively used as the reference voltage at the "+" input to the differential amplifier, while the "-" input is indirectly referenced to ground. In order to keep the two input voltages to the amplifier the same, the amplifier must set Vout to whatever voltage is required to make the feedback voltage to the "-" input match the input voltage to the "+" input.
http://www.play-hookey.com/analog/non-inverting_amplifier.html [Broken]
 
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  • #10
tim_lou said:
the class is designed for physics majors... it is just a part of the standard computer based lab for physics majors. the prereq. is just some freshman "modern physics" class... anyway.
so, I think I know what you are talking about... the T approximation or something like that? I think I got that one.

perhaps you can tell me what the op-amp is equivalent to in a circuit? (approximately?)

IMHO, I find it rather surprising that they would give a circuits lab without a proper circuits analysis course to complement it. Regardless of your major, you need to have the theory down before you can understand the lab. This is just bad planning on their part.
http://content.answers.com/main/content/wp/en-commons/thumb/1/12/450px-Opamptransistorlevelcoloredlabeled.png [Broken] is the schematic of a 741. So it equivalent to transistors, resistors, and capacitors in special configurations to perform the desired functions.
 
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  • #11
ranger said:
It is the bunch of uses for the op-amp that give rise to the numerous equations. There isn't any principle equation to relate those aspects that you've requested. It just changes from application to application. As for the gain for a non inverting amp, I'm afraid that it isn't the same principle for the other op-amp configurations.

really? looks like I'll have to memorize the results for inverting, non-inverting, instrumentation amplifier... and all the other good stuffs. the 741 does look like a complicated piece of device... Just hope my prof doesn't ask me to work out a circuit with a new configuration of 741s... :frown:
 
  • #12
There is no need to memorize everything. Invest some time to learn KCL and KVL. They will help you a lot. You can also apply these concepts to transistor circuits.
 

1. Why do I have to take a lab class for semiconductors and circuits?

Lab classes are an essential part of any science curriculum as they provide hands-on experience and allow students to apply theoretical knowledge in a practical setting. In the case of semiconductors and circuits, lab work is crucial in understanding the behavior and characteristics of these components.

2. What can I expect to learn in a lab class for semiconductors and circuits?

In a lab class for semiconductors and circuits, you can expect to learn about the fundamental principles and concepts related to these components such as diodes, transistors, and amplifiers. You will also gain experience in using equipment and techniques commonly used in the field.

3. I dislike working with circuits. Can I still do well in this lab class?

While it is understandable that some students may not enjoy working with circuits, it is important to remember that lab classes are designed to help you learn and improve your skills. With effort and dedication, you can still do well in this lab class and gain a better understanding of semiconductors and circuits.

4. How can I prepare for a semiconductors and circuits lab class?

To prepare for a lab class on semiconductors and circuits, it is important to review and understand the theoretical concepts related to these components. You can also familiarize yourself with the equipment and techniques used in the lab and read through the lab manual beforehand.

5. Will there be opportunities for hands-on experiments in the lab class?

Yes, lab classes for semiconductors and circuits typically involve hands-on experiments where you will have the opportunity to work with real components and equipment. These experiments are an important part of the learning process and will help you gain a deeper understanding of the subject matter.

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