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Regarding proctecting opamp against negative input

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sabu31

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Hello All,

I am using a current sensing IC ACS712 for sensing current in DC-link. I need to remove the default offset of 2.5V in ACS output using OPAMP MCP6022 (0-5V rail )and TL431 (2.5V ref).

However, for some time, there is a negative current. When I remove the offset using TL 431, the -ve current will result in -ve voltage. How can i protect opamp against this negative current? Will the circuit modification using diodes help to protect the opamp circuitry?

Or Else what alternative can be used for the protection of opamp.
 

Hi,

Show your circuit.
I don't get how can there be negative voltage at the Opamp input. The ACS712 can't generate negative voltage. So where does it come from?

Klaus
 

Hi,

Show your circuit.
I don't get how can there be negative voltage at the Opamp input. The ACS712 can't generate negative voltage. So where does it come from?

Klaus
ACS does not generate negative voltage. However, if i remove the offset of 2.5V using TL431. there will will -ve voltage due to the negative current
 

As your ADC can't process negative input voltage, your signal conditioning amplifier can be single supply with rail-to-rail output.
 

.... and you don't like to show us how you do this...

Klaus
Basically I intend to use this circuit. However, when i remove offset, what will happen to signal due to negative current
--- Updated ---

As your ADC can't process negative input voltage, your signal conditioning amplifier can be single supply with rail-to-rail output.
Do i need to add clamp diodes across the supply rails
 

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1. Protection may be needed against input voltage beyond the supply rails. If we don't know supply voltage, we can't know about protection requirements.
2. I don't see where protection should be needed in this circuit.
3. Consider that most OPs have substrate diodes that protect the input against overdrive as long as the current is limited to e.g. 1 or even several mA. Review datasheet if overdrive can occur in your circuit. As far as I see, it's not the case here.
--- Updated ---

Sorry I overlooked 0..5V rail spec in post #1. As said, no protection required here.
 
Hi,

I see it´s asking too much for a complete schematic with part values and power supply...
I don´t understand ... You just make it hard for yourself ... to get a clear answer.

Can you show/tell us a condition in this given circuit where negative voltage is at the OPAMP input?
As far as I can see there is no negative voltage at all. At least no negative voltage with respect to GND.

Klaus
 

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