Working of this OP-AMP circuit

[FreshmanNewbie]

In this Application Note, Section 4.2 GFCI Fault Detection and Test, page 14, can someone tell me the working of the circuit.



Unable to understand it.

 

[danadakk]

You read the application note, so what part do you not understand ?


Regards, Dana.

 

[barry]

First opamp is peak detector with gain of -100. Second opamp is comparator with, for some unknown reason, a diode on the output.

 

[KlausST]

Hi,

Same circuit as in your last thread.

Working of this protective circuit

Below is a circuit which I found that is used for Protective Earth Neutral detection. The PEN_ON comes from MCU and PEN_dET does to an MCU. P20, is a current transformer. Can someone explain me the working of this circuit and why it is required? This is an application of an EV charger...

www.edaboard.com

Klaus

 

[barry]

Is FreshmanNewbie the new Cupoftea/treez?

 

[FreshmanNewbie]

You read the application note, so what part do you not understand ?


Regards, Dana.

Thank you. In the second line of the paragraph, it is mentioned " A discharge path", can you tell me what is the discharge path? 2. Is the signal in GFCI+, an AC signal? 3. Why is there a diode in output of both the op-amps?

--- Updated Jun 16, 2023 ---

Hi,

Same circuit as in your last thread.

Working of this protective circuit

Below is a circuit which I found that is used for Protective Earth Neutral detection. The PEN_ON comes from MCU and PEN_dET does to an MCU. P20, is a current transformer. Can someone explain me the working of this circuit and why it is required? This is an application of an EV charger...

www.edaboard.com

Klaus

Thank you. In the second line of the paragraph, it is mentioned " A discharge path", can you tell me what is the discharge path? 2. Is the signal in GFCI+, an AC signal? 3. Why is there a diode in output of both the op-amps?

--- Updated Jun 16, 2023 ---

First opamp is peak detector with gain of -100. Second opamp is comparator with, for some unknown reason, a diode on the output.

Thank you. In the second line of the paragraph, it is mentioned " A discharge path", can you tell me what is the discharge path? 2. Is the signal in GFCI+, an AC signal? 3. Why is there a diode in output of both the op-amps?

 

[danadakk]

https://ww1.microchip.com/downloads/en/appnotes/01353a.pdf

First OpAmp acting as a FW rectifier.

The discahrge path is for C3 back thru R59, R10, R14,.

GFCI - https://home.howstuffworks.com/question117.htm


Regards, Dana.

--- Updated Jun 16, 2023 ---

Something like this :

Regards, Dana.

 

[barry]

https://ww1.microchip.com/downloads/en/appnotes/01353a.pdf

First OpAmp acting as a FW rectifier.

View attachment 183408

The discahrge path is for C3 back thru R59, R10, R14,.

GFCI - https://home.howstuffworks.com/question117.htm


Regards, Dana.

--- Updated Jun 16, 2023 ---

Something like this :

View attachment 183411


Regards, Dana.

Its a half-wave rectifier, not full-wave (still, maybe a peak detector, depending on how you look at it)

 

[danadakk]

The ap note seems to indicate, rightfully, its FW :

It uses the diode for one phase, the OpAmp as a sign changer for the other.


Regards, Dana.

 

[barry]

The ap note seems to indicate, rightfully, its FW :



Regards, Dana.

Not with those component values. It's got a gain of 100 in the negative direction. A gain of 1 in the positive direction.

Rerun your simulation without the cap and see what the output looks like.

 

[danadakk]

@barry

I completely misinterpreted that ap note, frankly got lazy, threw investigative
thoroughness out the window. Even I noticed imbalance in sign changer G,
eg. could not function as that, and then promptly forgot to go back and look
at it again. Thanks for hauling me up by the short hairs.

The sim does not seem to work with or w/o cap, makes no difference,
and sim output just looks odd.

It does, however, seem to indicate a simple peak detector from output view
with 10 uF. It just pumps up cap and the slow leakdown rate thru fdbk R
essentially holds the charge.


Regards, Dana.