Why does a clamper circuit shift the input voltage upward by 20V?

[Abdulwahab Hajar]

Hello everyone, I hope you could help me with the analysis of this circuit.
the output voltage is supposed to be similar to the input but shifted upwards by 20V, so basically it's between 0 and 40V... but why?
I mean when the input is 20V, the diode is reverse biased... and the capacitor charges... our output voltage depends on the ratio of the resistance to the capacitive reactance... at least until the capacitor fully charges... but then what happens?

Thank you

 

[jim hardy]

I mean when the input is 20V, the diode is reverse biased... and the capacitor charges...

no. They told you the time constant is large, so the capacotor does NOT charge through the resistor.

Your thought tool should be this: "Time constant is large, eh? If i take that to the extreme how would the circuit behave? Limit would be infinite time constant... so what would go on if that resistor were nearly ∞ or not even there ? "

In your mind snip out that resistor and repeat your thought experiment , considering both Vt transitions.

 

[Abdulwahab Hajar]

no. They told you the time constant is large, so the capacotor does NOT charge through the resistor.

Your thought tool should be this: "Time constant is large, eh? If i take that to the extreme how would the circuit behave? Limit would be infinite time constant... so what would go on if that resistor were nearly ∞ or not even there ? "

In your mind snip out that resistor and repeat your thought experiment , considering both Vt transitions.

I really can't see where this is going, a bit more insight would be highly appreciated...
I mean a very high resistance would mean almost 0 current given that the voltage supply is constant... but that doesn't really get me anywhere..
Also sir, they said that the time constant is large... how would we know if that indicates a large resistance or a large capacitance.. since the time constant is RC and dependent on both...

Thank you!

 

[jim hardy]

I really can't see where this is going, a bit more insight would be highly appreciated...
I mean a very high resistance would mean almost 0 current

What about the diode ?

 

[jim hardy]

the voltage supply is constant

??

looks to me like voltage goes from +20 to -20 then back to +20, maybe repeating that forever they didn't say .

You are not operating the circuit in your mind.

 

[Tom.G]

Here is a video that may help. The presentation is not the best, he rushes thru the explanation with an accent so you may have to backup and repeat parts of it.



Above was found with:
https://www.google.com/search?&q=voltage+clamp+-cell+site:youtube.com

 

[Abdulwahab Hajar]

Here is a video that may help. The presentation is not the best, he rushes thru the explanation with an accent so you may have to backup and repeat parts of it.



Above was found with:
https://www.google.com/search?&q=voltage+clamp+-cell+site:youtube.com

The video was great thank you! Completely got it

 

[Abdulwahab Hajar]

What about the diode ?

Got it sir, I forgot that the diode would determine the voltage drop Vo...
Thank you!