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[SOLVED] Half Wave Rectifier when input voltage is negative

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dzafar

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Hello,

I am new to half-wave rectifiers. Below is a screenshot from my book.

Untitled.png

Can someone please explain why VOL is 2V greater than VEE?


Thanks!
 

Hi,

One need to know the Opamp type and read it's datasheet.

Klaus
 

Suppose I have an LM741 op amp. What should I look in the datasheet to get that information?


dzafar
 

Hi,

Usually it is given as "V_OL"
But in case of LM741, look for "output voltage swing"

Klaus
 

Can someone please explain why VOL is 2V greater than VEE?

Most modern op-amps can get you rail-to-rail output. Well, I meant many.
 

The design of the lousy old 741 opamp is 50 years old and its designer never dreamed that an opamp will have a saturation voltage that is less than 2V.
 

the lousy old 741 opamp is 50 years old...

If you are at least as old as me, you will know the electronics state of the art those days! It was not only expensive but was considered a gem.

The application notes ran for pages and we wondered what it cannot do! I even saw a few audio power amplifiers made around the venerable 741.

These days students are not taught Thevenin or Norton or the superposition theorems (they learn everything on the fly at the forums) but they looked scary in the exams.

Perhaps I have become lousy old one. But everyone had its own day.
 

The design of the lousy old 741 opamp is 50 years old and its designer never dreamed that an opamp will have a saturation voltage that is less than 2V.

Although rail-to-rail output is nearly a standard in general purpose OPs these days, you still have specialized devices that can't achieve it due to a different performance trade-off, e.g. GHz OPs. In so far, it's necessary that an analog designer understands about input and output voltage ranges and impact on circuit design.
 

The 741 opamp was spec'd to use ONLY a plus and minus 15V supply because its input and output voltage ranges were low and its gain dropped when the supply voltage was reduced. It is too noisy for audio and cuts frequencies above 9kHz at high levels since its slew rate is poor. Modern audio opamps are commonly used resulting in low cost and have low distortion and low noise. Many work fine with a supply of only plus and minus 3V and produce full output to 100kHz or higher.
 

Hi,

I conclude that the 741 is a staple of "every" OA tutorial, and book or lecture because it is actually, in it's monolithic "rubbishness", an excellent teaching and learning aid to understanding op amps from the word go - it even has offset null pins. What's mid supply output, offset error and phase reversal, then if you've never been exposed to the veneerable 741?
 

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