Op amp clipper issues

I am guessing that the current drawn from the amp due to clipping heats up the chip enough to cause that verdammdt shutdown. I refuse to use any device with internal temperature shutdown; it causes more pains that the resulting "safety".

What is your supply voltage. Should that chip be hot? How much power the IC dissipates.

Post a schematic. Either here using ASCII art, or on flikr, or something.

ng.

ttdesign.com

I did. Just read what I said and you should get it. The schematic is exactly as I have described in English. That should be enough unless English is not your first language? Do you have issues with mathematical word problems too?

I guess I need to scope it to find out what exactly is going on. What strange to me is that it seems to work when the gain is higher which should cause it to use more current. There could be something else going on like power loss to the op amp as do have a rather high impedance power source but the op amp is bypassed. Again though, I would expect the exact same issue at high gain?

Well, I guess _you_ aren't really interested in getting help, here.

you'd have the chip let out the smoke?

-Lasse

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cottdesign.com

you always reply like that to people who is trying to help you?

a part number and a schematic would help

-Lasse

Smug little SOB from googlegroups... already kill-filed.

I always wonder what possesses people like that who presume they are _owed_? Probably a leftist weenie ;-) ...Jim Thompson

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cottdesign.com

Wow! And you expect help? You'll catch more flies with honey than vinegar.

George H.

"Abraham"

When low frequency signals come along and are clipped by the diodes, smaller mid and high frequency signals are severely attenuated.

If only signal peaks are clipped, nothing like this occurs.

If the whole signal is severely clipped, the output level stays steady.

A scope will show you all these things happening.

A fix might be to filer the low frequencies out.

... Phil

"Phil Allison"

Lose to 100 ohms resistor and put in a 1000 ohms.

.... Phil

I bet it is something like this too. It is almost surely a loss of bias or supply voltage since transient clipping will not cause the op amp to shut down except in rare cases. Since this seems like an audio circuit I would check the coupling capacitor as it could be losing bias causing the signal to flatline. If it has the proper bias across it I would then expect the op amp/power assuming there is nothing else in between.

amp

op

I think I might have a bad board. The coupling capacitor does seem to change a lot when the clipping is connected. Whats stranger is that if I blow on the board I either get a high pitch squeal or it completely shuts off. I think it maybe the rail splitter. Maybe it is bad. When I blow on it or on the clipping diodes is when I get the problem. I've never experienced issues by just blowing on it. None of the components are hot but something must be bad or wired up wrong. The rail splitter does split properly. Looks like I'm going to have to spend some time finding the culprit ;/

Its my guess the circuit is oscillating at the troubled gain select.

Jamie

yes, you got yourself I nice RF detector..

Jamie

Temperature shutdown is put in to protect the part. Most final products, that is in the hands of the user, will never trip the shutdown. But the oaf designer shorting pins with a scope probe could trip the shutdown. The goal is to prevent the part from failing in the design process. If a part croaks in the design process, the oaf will never admit to abusing it, but will probably pick a different part instead.

If it makes you feel any better, nobody really like to design thermal shutdown protection. If you screw up and it turn on under normal operation, you catch crap. If it turns on at too high of a temperature, you catch crap. If the models suck at high temperature causing the design to be incorrect, the designer still catches crap.

These thermal shutdown circuits usually have a lot of black magic in them in the way of replica devices to insure leakage paths balance out.

Thermal shutdown is bench tested and QA tested (if your lucky). I don't know of any semi that 100% tests thermal shutdown. Current limiting protection, also put in many chips though not always stated in the datasheet, is 100% tested.

Thus this chip could be hitting a current limit in the design or temperature.

When you clip the amp, you break the feedback path. That could lead to "sticking", but not for a second.

If the negative input to the op amp is going to the diodes, then you are ripping the differential pair apart. If you take the feedback right from the op amp output, then this is less likely to be the case.