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LM386n datasheet inquiry

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bitman:
For a few days I was lost trying to get a very simple LM386n circuit to work - took me a while to realize a simple wrong connection - but it led me to read the datasheet in details.  Now that I finally got the simple 20x and 200x circuit to work, I'm seeing characteristics I cannot find in the datasheet.

The biggest issue and the reason for my question is, that it look like when the amplitude reaches 5V on the output, the LM386n just stops amplifying. I see a flat top if the input is larger. The lowest voltage amplitude my function generator can make is 0.5v so that should be +/- 0.25v which is well within the +/- 0.4v on the input. I have to admit that during my tests I far exceeded this so perhaps my just destroyed the chip.  Anyway, I cannot find where in the datasheet such a limit exists.  0.4*200 is far above 5V it cannot be inferred. 

Other beginner issues and lessons learned is:

* Supply voltage isn't the max amplitude this chip can provide. I started out with 5V on the Vdd and nothing worked. It wasn't until I put that at 9v my very low < 0.5v input signal was amplified.
* "Cheap" scope (Rigol DS1054Z) cannot trigger on very low voltages. When the amplitude gets below 0.15v or there about it will no longer trigger.  I wonder what specs states how sensitive the scope is - not a big deal, but it's definitely nice to know going forward.

Hopefully someone can help explain what seems to be basic to a lost novice.

bdunham7:
Could you post your circuit?

Some of your conclusions are wrong and I'd like to see how you arrived at them.

1) the DS1054Z will trigger just fine far below 150mV--actually I'm not sure exactly what you mean.  Default trigger is zero.
2) supply voltage does determine the max amplitude, but it would be peak-to-peak, minus a bit, not RMS.  Do you have an output capacitor?

As you've figured out, your input voltage is way too high to properly set up an amplifier circuit with this IC, even with max Vss and default gain.  The solution is simple--you need an input voltage divider AKA volume control.  The datasheet should have example circuits.

Zero999:
It's clipping. The maximum peak to peak output voltage is limited by the power supply voltage and the losses in the LM386's output transistors.

If your function generator can't produce lower voltages, then you need an attenuator on the output. A simple potentiometer will do, but I advise building one with a rotary switch and some resistors to attenuate by a factor of 10 or 100.

bitman:

--- Quote from: Zero999 on May 26, 2019, 05:56:20 pm ---It's clipping. The maximum peak to peak output voltage is limited by the power supply voltage and the losses in the LM386's output transistors.

If your function generator can't produce lower voltages, then you need an attenuator on the output. A simple potentiometer will do, but I advise building one with a rotary switch and some resistors to attenuate by a factor of 10 or 100.

--- End quote ---

I've got a 10k pot on the input - as indicated in the datasheet. This is how I know that when I get a signal less than ~150mV the scope no longer auto-triggers. It's also how I see the output get capped at 5V amplitude when I turn the input voltage amp up.

Since you didn't say "yeah, that's correct" in regards to my observation on the output max amplitude, given http://www.ti.com/lit/ds/symlink/lm386.pdf section 9.2.2 (that's my circuit) and let's make the Vdd 12V - are you saying I should be able to get more than 5V amplitude with a 200mV amplitude input and a 200 gain? I do not see that.

Audioguru:
The datasheet shows the test circuit with a 10k volume control at the input pin 3 to ground, pin 2 is grounded and a 250uF capacitor feeds an 8 ohm speaker. The input to the volume control must be audio with no DC voltage on it so that pin 3 averages 0V.

The graph on Page 4 Peak-To-Peak Output Voltage Swing Vs Supply Voltage shows the maximum output voltage swing at different speaker impedances and different supply voltages. With a 5V supply the maximum output is 3V p-p which is +1.5V and -1.5. If the output is more than 3V p-p then the top and bottom of the waveform will have flats that we call "clipping" and it produces severe distortion.
When the gain is set to 20 times then if the input level exceeds 3V/20= 0.15V p-p then the output will be clipping.
If the gain is set to 200 times then if the input level exceeds 0.015V (15mV p-p) then the output will be clipping.
3V p-p into an 8 ohm speaker is a power of 0.14W which will be distorted a little and is so low that it is almost nothing.

If a 9V supply is used then the maximum output level will be 6V p-p and the power in an 8 ohm speaker is 0.56W like a cheap clock radio.

Please post a schematic of your circuit showing all parts values, the supply voltage and the speaker impedance.
Here is what amplifier clipping looks like on an oscilloscope:

     

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