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yellow channel is from lm386 amp 20 times gain yellow channel is from lm386 amp 20 times gain

my circuit is from the lm386 datasheet with 16 V source, what i amplify is 40khz arduino pwm output, is there any explanation why this happened, thanks

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  • \$\begingroup\$ Welcome to EE.SE. Only the best audio gear can handle 40 KHZ, and the LM386 is not one of them. Poor rise and fall times plus phase shifting. You need a RF or wide-band pulse amplifier. Look into the OPA 357 series. Link:ti.com/lit/ds/sbos235e/sbos235e.pdf That is a suggestion only, as some of these op-amps are expensive. \$\endgroup\$ – Sparky256 Mar 13 '18 at 4:52
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    \$\begingroup\$ You need much wider bandwidth than 40kHz for a 40kHz square signal. \$\endgroup\$ – Chupacabras Mar 13 '18 at 5:21
  • \$\begingroup\$ isn't LM386's bandwidth 300khz? \$\endgroup\$ – Mbahjiman Mar 13 '18 at 5:39
  • \$\begingroup\$ Small signal yes , But input is saturated and output slew rate is limited You probably want 10V/us min at some current? \$\endgroup\$ – Sunnyskyguy EE75 Mar 13 '18 at 5:54
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The waveform distinctly shows that the LM386 is not an amplifier with the bandwidth or output slew rate capable of amplifying your input waveform that has basically square edges.

The LM386 is considered to be an audio power amplifier which would mean that it would be typically capable of handling sine wave type audio frequencies from about 100Hz up to about 20kHz in a real application.

The part is speced to have a bandwidth of typically 300KHz when the gain is at its default level of 20. Of course that is for sine wave signals. At the large wave signal you are feeding you will come no where close to that.

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Depending on your requirements, it may be smart to go with just a simple single-transistor switch like the one shown below:

schematic

simulate this circuit – Schematic created using CircuitLab

Keep in mind that the output will be inverted! If this is a problem, you can either invert the output of the micro somehow, or add another one of the 'invertors; in. I believe it's both cheaper and probably better suited for what you intend to do than the LM386!

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