Electrical Engineering Letter Exchange
(for engineering majors in other areas)
9/22/88

A Note on Difficulties with Rectifiers, Amplifiers,and Phasors

My problems with rectifiers, amplifiers, and phasors are basically conceptual, and, as a result, difficulties arise in problem solving techniques. Perhaps just by taking the time to write down and define my problems, I can collect my thoughts on this subject and,
in effect, answer some of my own questions.

I really don't have a problem with the rectifier. I know there are several types that I need to know how to use. The rectifier is just a means of converting AC to DC. Filters are used in conjuction with the rectifier to decrease the magnitude of the AC ripple. Overall, I feel pretty comfortable here.

Op-amps are creating a problem, though. First of all, how can you tell if the amp is inverting or non-inverting? And also, what exactly do "inverted" and "non-inverted" mean? Does "inverted" mean that the sinusoid function is inverted in exit from the amp? I find this very confusing. Perhaps you know an easy way of remembering what's going on-I don't!I think that I have an idea about phasors.

But, I might be wrong. Do phasors represent a correlation between the current and the voltage sinusoid function?It seems that this is the case in Lecture #10, page 7. However, on Lecture #10, page 6, you find the total AC voltage across the two impedences. How does this include the idea of phasors? Perhaps just a good definition of the phasor willl help most.Thanks for your help.

Ben

To: Ben Sept. 27,1988
From: Michael
Subject: Difficulties w/ amplifiers, rectifiers & phasors

Ben, I have read your memo dated 9/22/88 and I believe I can offer some help in the area of amplifiers and phasors. In order to tell what type of op-amp circuit you have, note the connection to the positive terminal on the amplifier and the positive terminal of the power source.

If the positive terminal of the op-amp is grounded and the input resistor is connected with the positive terminal of the current source, you have an inverting op-amp circuit. In the non-inverting. op-amp circuit the input resistor is grounded and the positive terminal on the amp is in series with the positive terminal of the current source. The result of these circuits is that the output voltage is inverted for the inverting op-amp circuit. The non-inverting op-amp circuit does not invert the output voltage. The method of connection determines the gain and consequently the output voltage of an amplifier (see below).

A phasor (for circuit analysis) is a transformed function of time into a complex constant that retains the simple information: effective value and phase angle. Phasor diagrams permit a picture of physical relationships that is not provided by algebraic solutions alone (i.e. voltage and current relations). Lecture 10, page 7 of the notes is a good example of a phasor giving us not only a physical diagram of the combined potential, but also a method of solving the problem mathematically.I hope have been able to help in your understanding of op-amp circuits and phasors.

—courtesy of Art Young, Clemson University