Any Op-amps with internal input protection?

[Electric-Gecko]

Does anyone know of any op-amps op-amps that have integrated overvoltage protection and/or biasing of the inputs?   It should be not too expensive, DIP/through-hole, and available somewhere like Digikey or Mouser.

The problem is, I go through way too many op-amps while prototyping pedals.  It only takes one mistake to quickly destroy them.  Sometimes I accidentally leave one of the inputs floating.  Sometimes, I forget to power it off when I change something in the breadboarded circuit.  They're probably getting destroyed by latch-up.

The input protection would probably be something like the following.  Overvoltage protection often uses Schottky diodes.  The biasing resistors would be great as well.


So does anyone know of an op-amp available with either of the features I described?

[antonis]

Can't help you - my knowledge is limited to "ancient" amps..

As far as it concerns prototyping, you may readily have a protection circuit to "snap" on any availiable amp you use...
(although it could be obtained with ordinary Si diodes and much lower resistors - depending on the specific op-amp of course..)

[anotherjim]

Yes, some already do - not sure offhand which ones & could be most of them - try the DMM on Diode function to check for a diode between the in or out pins and both supply pins.

However, the protection diodes need help - you can insert series resistance immediately or somewhere before the pin. The resistance reduces the fault current when the diodes conduct. Many designs do this.

That said, it's really only done on input and output of the whole circuit, it shouldn't be needed interstage unless you're worried about flyback from an inductor.

I suggest you also consider if you could have a static discharge problem, because most op-amps are fairly robust.
I'm sure we all make handling mistakes when breadboarding, but don't fry the chips in the process. So far I've found an MC1458 and LM358 that I think I may have killed, but I'm not certain how - that's 2 chips out very many over recent years.

[merlinb]

most op-amps are fairly robust.

+1. What are you doing to these poor ICs?!  Opamps are hard to kill, especially in wussy 9V stomp box circuits!

[PRR]

All opamps to the '709 have input protection. All opamps after the 709 have output protection.

So what are you doing??

A many-uFd cap direct connected to an input, while a loaded power supply goes down, will pass current through the protection diode to the load the power supply is no longer supporting, and would blow the protection.

I think the last opamp I killed (not counting the dozen my friend connected reverse-supply) was a '709 output short, back in 1974.

If you want to change spark-plugs, stop the engine!! Otherwise you will be sorry somehow.

[Electric-Gecko]

What are you doing to these poor ICs?!  Opamps are hard to kill, especially in wussy 9V stomp box circuits!

Probably the most common is when I occasionally make the mistake of leaving an input open (floating).  That problem would be solved if it had integrated biasing resistors (of high value).
I also sometimes forget to unplug the power when I insert or remove an op-amp.  But it would be an advantage even if it only solves the first problem I mentioned.

Most of them have been TL072 & TL074, but also JRC4558D (which I might not use again) and LM5532.

[PRR]

Floating input should not be a problem unless you wear silk while rubbing the cat with amber (static discharge).

"Floating" meaning a large cap and no discharge path could be bad. The cap would charge through chip leakage, then discharge back through the input when the power supply goes down.

But you have been remarkably unlucky. Maybe time to work more carefully.

How sure are you that these chips are dead?

[anotherjim]

Self biasing op-amps are few and far between, and not really op-amps even though the circuit symbol looks like one. A common example is the LM386 power amp.
Internal bias resistors - I don't see how these could protect, unless of such low resistance that they would seriously effect the circuit design.
As I said earlier, but in a different way, internal chip protection diodes cannot protect if sufficient current flows that the diodes themselves are damaged. As they are formed in the same substrate as the main circuit, damage to the diodes usually means the chip itself is destroyed. How would bias resistors stop that?
The protection diodes won't work properly if there isn't a power supply connection or else where do they conduct fault current to? In fact, they can feed power to the chip until excess current blows them.

Some op-amps have clamping diodes or transistors between the + and - input pins, so the pin voltages cannot get too far apart (This type of chip can be damaged if there is excessive difference in voltage between + and - pins). I think the 5532 is an example of these. Like protection diodes, they must not be allowed to pass excessive current or the chip is damaged.

Series resistance is the way to protect inputs from excessive current.

So you could fit 10k (or 1k) resistors in the BB between the input pins and whatever is there in the existing circuit. Most opamps have such high input impedance that 1k or 10k (higher is safer) won't change things more than add a little noise. Some audio grade types like the 5532 do not have such high input impedance, so use 1k.

[antonis]

Probably the most common is when I occasionally make the mistake of leaving an input open (floating).

If you refer to unused part inputs (of dual or quad amp) it may lead to oscillation or other "strange" things but definately NOT to damage ..

I also sometimes forget to unplug the power when I insert or remove an op-amp.

Excuse me but you're searching for some scatterbrainded-friendly design Op-Amps..