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what is the simple difinition of voltage swing

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Newbie level 3
Jun 17, 2011
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i have been asked so many times the meaning of swing in op-amp741 of my teacher but i realy do not undrestand and i dont know which kvl is the true kvl ?is this ture that we have to choose the nearest way to Vout from Vcc?
i would be so happy if you could explain this for me:?: thank you

Swing is the difference of maximum output voltage and minimum output voltage. Maximum possible swing in output you can have is VDD-VSS. where VDD is most positive voltage and VSS is most negative voltage. It does not mean that your swing is VDD-VSS. It may be smaller than this. This depends on circuit design.
For CMOS logic family it is VDD-GND. It means CMOS logic family have full voltage swing.
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sorry again i don't undrestant ,for example in op-amp741 why Voutmax= VCC-Vce(sat)13-Vbe14 ? why it isn't:VCC-Vce(sat)14? thank you

The output circuitry of op-amps have one transistor pulling the output pin up to +Vcc and another transistor that pulls the output pin down to -Vcc. So the output pin can only go to Vcc - VCE sat in each direction. It is unusual to run a "linear" amplifier right up to the output transistors saturation point, because the risk of lock up (negative feedback turning into positive), so it is safer to allow a margin between the Vout and the VCC.

You should clarify which transistor level 741 circuit you're referring to.

I don't understand what you mean with "choose the nearest way"? In my opinion, you need to understand the operation principle of the output stage. Voutmax= VCC-Vce(sat)13-Vbe14 is in fact correct. It's obvious, that the Q14 base node will be always higher than Vout by one diode voltage drop. But you have to check, if Q13 can achieve saturation or if a concurrent path will possibly drain the current source output.

The voltage swing refears to the output voltage swing.
That means tha maximum variation of voltage at the output stage of the opamp and it is not VCC or VDD that is because the output stage of the opamp is made of transistors andthey need bias voltage so it is Vcc minus some voltage aprox 1.2V and Vdd plus 1.2.
If your bias voltage is +18 and -18, your voltage swing is between (+18-1.2= +16.8V) to (-18+1.2 = -16.8V) and you cannot obtain a voltage above or below that limits.

Voltage swing is just an English term widely used by engineers, describing the voltage level going up and down. Like having been said, it usually implies the difference between the highest and the lowest in voltage that the system operates.
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thank you all, and tomorrow i have the exam and i think that i have understood the meaning

---------- Post added at 12:36 ---------- Previous post was at 11:37 ----------

i asked this to my freind and she answered "choose the nearest way" , and as you explained i understood it is'nt correct ,also i dont understood you said "which transistor level 741 circuit you're referring to"?
i meant the Building Interior of op-amp741 ,if i dont make mistake ,and thank you for your help.

i meant the Building Interior of op-amp741
Different schematics have been published by manufacturers and in text books, device numbering is partially different.

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