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will an Op Amp be damaged if input voltage is higher than supply?
John_doe:
Sorry for the newbie question, I have googled this and found a plethora of answers, however, either none of those that I read answered my specific situation, or they did but I didn't understand the explanation.
My question seems pretty straightforward: If I supply 20Vdc to the non inverting input of an LM358 configured as a unity gain voltage follower, and supply it with only a single 5.5Vdc source, will the LM358 be damaged?
I am NOT asking if the Op Amp will work, only if it will be damaged.
If the answer is "Yes", additional questions:
1. Is there another Op Amp model that can be used this way?
2. What if V+ (positive supply) is not connected at all, will this help?
If the answer is "No", additional question:
1. Can the Op Amp output exceed 5.5V ?
Note: If it helps R1 and R2 can be increased to 1M.
Alex Nikitin:
You should learn to read datasheets carefully - all this information is there. For the LM358 the maximum input voltage (without damage to the device) could be up to +32V from the negative supply rail, independent from the actual supply voltage, so for this particular opamp and circuit it is perfectly safe to put +20V on the input with only 5.5V supply.
Cheers
Alex
Peabody:
This is what the Absolute Maximum Ratings section of the datasheet is for. Surprisingly, it appears you can apply up to 32V to an input without damaging it, and it also appears the maximum is not related to the power supply voltage (it often is), which is also 32V maximum.
However, the output voltage can never exceed the actual power supply voltage, 5.5V in your case. It will actually be a bit less than that, and this will also be described in the datasheet.
If it could output 20V, then you would run up against the maximum ratings of the 328P's A0 input, which is less forgiving.
rstofer:
However, the output voltage can not exceed the upper rail voltage. See the schematic on page 20 here:
https://www.sparkfun.com/datasheets/Components/General/LM358.pdf
And why would you want a high voltage output? The maximum analog input to the ATmega328p is Vcc + 0.3V Page 325 here:
https://www.sparkfun.com/datasheets/Components/SMD/ATMega328.pdf
It would seem to me that the graph of Input Range in the upper left corner of page 6 of the LM358 datasheet limits the input voltage to be <= absolute value of the respective rail voltage. For negative inputs, the voltage can closely track the V- rail but for positive inputs, the voltage must be somewhat less than the V+ rail. So, while using high voltages may not destroy the device, I certainly wonder if the op amp works under the stated conditions.
iMo:
The inputs of an opamp (and other chips as well) are protected by clamping diodes (2 or 4) and a resistor, something like 200-400ohm. That is the basic ESD protection.
Opamps usually have got another diodes in between the INV and NINV inputs.
In case the voltage at an input is higher than Vcc or Vss, the respective diodes start to conduct, and they divert the current into the Vcc or Vss.
The diodes can usually survive 5mA.
It depends on how you LIMIT that current.
When you have external resistors wired at the inputs, for example 10k, the max voltage which will not smoke the ESD diodes would be
Vmax_input = Vcc (or Vss) +/- 0.6V +/- 0.005A*10k
That would work when the LM358 has got an ESD protection.
PS: better go with 1mA when doing the calculation :)
https://www.analog.com/en/analog-dialogue/articles/esd-diodes-as-voltage-clamps.html
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