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LM358 one opamp fails Please sugest what to do..

gurbir

Jun 11, 2017
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Sir Please suggest :
LM358 UB is getting damaged 2 out of 10.
R12 = 100E
R16,11,14,23 = 150E
R24,10 = 4K7
R18,19 = 10K
 

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Audioguru

Sep 24, 2016
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Your schematic is not finished yet since the resistor values are not printed on it.
The LM358 cannot be damaged in your circuit because there is no input voltage.
The datasheet says the input must never be more negative than -0.3V or more positive than +32V.
The datasheets are powered by 8V. Is it 8VAC, -8VDC or +8VDC?
VCC has no voltage shown that might be too high or might be AC or negative.
 

gurbir

Jun 11, 2017
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input voltage 75mV, (its DC ampere meter ckt. CT1 & CT2 are 75 mv shunt terminals )
resistances values are
R12 = 100E
R16,11,14,23 = 150E
R24,10 = 4K7
R18,19 = 10K
Vcc is 3.3Volt DC
one opamp damaged only, circuit is working ok but 1 or 2 out of 10 are damaged
 
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BobK

Jan 5, 2010
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You show two unconnected inputs. The difference may be 75 mV as you say, ut what about the voltage with respect to ground? Is there even a common ground between your circuit and the source of the inputs?

Bob
 

gurbir

Jun 11, 2017
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Thanks for reply.
This is ampere meter ckt. enclosed in panel mounted 96*96 mm plastic encloser. No there is not common gnd. between my ckt and sourse of inputs.
Mostly input source is 0 to 75 mv SHUNT connected in industrial rectifier (say 12 v 1000 amp to 12 v 1000 amp or 400 volt 5 amp to 400 volt 50 amp ) .
Shunt may be either in +ve side or -ve side.( mostly in -ve side)
 
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Harald Kapp

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one opamp damaged only, circuit is working ok but 1 or 2 out of 10 are damaged
When was the opamp damaged? After connecting the circuit to the shunt resistors or before? Could the damage be a result of poor soldering?
In which way is the opamp damaged? No gain or wrong gain?
Mostly input source is 0 to 75 mv SHUNT connected in industrial rectifier
When you say "mostly", this sounds that there is a chance of the input voltage being much higher, e.g. in case of an overcurrent. Your circuit has no input voltage limiting. Is there an external limiting circuit? If not, I recommend you add one, for example using diodes like this:
upload_2017-6-12_8-26-55.png


I think we need a bit more information for a better analysis.
 

gurbir

Jun 11, 2017
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This is my question when the opamp damaged. I could not come to know yet.
But it dameged After connecting the circuit to the shunt resistors in field at first 1 day or during installation of rectifier (machine).
No not due to poor soldering. Because am using same ckt. in volt meter also with changed resistor values (1.5 meg instead of 150 ohm) volt meter working 100% ok not even 1 faild out of 500.
Dameged opamp gives max. out put i.e. 7.5 volt even input (Shunt wire)open.
Sir i used antiparallel 1n4148 at pin 5 and 6 of LM358. i also changed res values 150E to 680E and 4K7 to 22K but result the same.
 
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(*steve*)

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Does the input float with respect to the ground of your power supply?

Looking at this circuit, it should. If it doesn't you could have problems.
 

gurbir

Jun 11, 2017
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Sir,
Input side is non floating.{ according to my knowledge non floating supply is one (-ve ) terminal connected with earth }
My ckt. is floating ground. its power is through isolated step down transformer .
 

(*steve*)

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My ckt. is floating ground. its power is through isolated step down transformer .

Then you should remove the earth symbol you show in the schematic :) (unless it's required to make the simulation work).
 

gurbir

Jun 11, 2017
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Sorry Actually it is really power plan part of pcb software..
 

Harald Kapp

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Show us the full schematic diagram including power supply and the connection to teh sense resistor, please.
What is R21 doing next to D2?
 

gurbir

Jun 11, 2017
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T1 is simple transformer its primary side pins are shown gnd are only for mounting purposes. direct wires are connected to connector.
 

gurbir

Jun 11, 2017
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Please suggest
- If i put LM358 pin 7 to gnd with 10K resistor.
or
- if i put 10K resistor between pin 5 & 6.
or both
what will be its effect will it be made non floating gnd??
 

Harald Kapp

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Try much higher values for R10, R11, R23 and R24, in the range of a few 10 kΩ, e.g. 15 kΩ and 475 kΩ.
It is possible that the 'machine' your circuit is connected to generates high voltage spikes which can destroy the opamp. High value resistors can protect the opamp.
Also increase R14 and R16 from 150 Ω to e.g. 15 kΩ. Note that you need to decrease the capacitance of C13 proportionally to keep the rolloff frequency of the filter at the same value.
 
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gurbir

Jun 11, 2017
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Thanks for reply
If I goes to K Ohm Ckt starts pick noise signals. like if we on any smps in same line ( same phase 220v aux. of meter) ckt start error . ckt changes its reading say from 800 to 825.

One thing i can't understand that when there is already 100 E resistor at input terminals how LM358 damaged.

Please suggest
- If i put LM358 pin 7 to gnd with 10K resistor.
or
- if i put 10K resistor between pin 5 & 6.
or both
what will be its effect will it be made non floating gnd??

or kindly suggest your design
 

Alec_t

Jul 7, 2015
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Mostly input source is 0 to 75 mv SHUNT connected in industrial rectifier (say 12 v 1000 amp to 12 v 1000 amp or 400 volt 5 amp to 400 volt 50 amp ) . Shunt may be either in +ve side or -ve side.( mostly in -ve side)
If either the 12V or 400V is referenced to ground then your CT1 and CT2 inputs could be above your opamp positive supply voltage or below its ground rail. The opamp won't like that.
 

Harald Kapp

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if that means 100 Ω, it won't protect the opamp from high voltages as can be generated by an electrical machine.
If I goes to K Ohm Ckt starts pick noise signals.
Increase the filter capacitance to remove the noise.
if i put 10K resistor between pin 5 & 6.
this will not help. The inputs of the opamp can still experience overvoltage.
If i put LM358 pin 7 to gnd with 10K resistor.
... I don't see how this should help neither. You're loading the output of the opamp but this is no measure to protect the input.
 

gurbir

Jun 11, 2017
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extremely big thanks to all for support ill try this and revert
 
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