What is the function of capacitors in this circuit?

Discussion in 'General Electronics Chat' started by Yaşar Arabacı, Nov 30, 2014.

  1. Yaşar Arabacı

    Thread Starter Member

    Nov 11, 2014


    I was wondering what is the purpose of 0.05uF and 250uF capacitors in above circuit. I built that circuit without using those capacitors and with capacitors that have similiar capacitance to those (because I didn't have those exact capacitors at the time) and circuit works with or without those capacitors. On the other hand, I would imagine they have some kind of purpose?

    Edit: By the way, my 470uF that I tried instead of 250uF was polarized, can that be a problem?
  2. MrChips


    Oct 2, 2009
    The 0.05μF capacitor in series with the 10Ω resistor is there to suppress high frequency oscillation of the amplifier. In most cases the circuit will work fine if you choose to omit both of these components (the 0.05μF cap and 10Ω resistor).

    The 250μF capacitor in this situation is called a DC blocking capacitor. The voltage at the output, pin-5 of the amplifier is at about Vs/2.
    Without this capacitor, the output would be shorted to ground through the loudspeaker. The LM386 will draw excessive current, the speaker could be blown and the circuit wouldn't work.

    This capacitor is also a high pass filter and sets the low frequency cutoff point. With 10μF you will be eliminating most of your bass frequencies. Going higher than 250μF gives you improved low frequency response.

    Capacitances at these high values are more readily available as polarized electrolytic capacitors. Make sure you connect the positive lead to pin-5. The negative lead goes to the speaker.
    Last edited: Nov 30, 2014
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  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    The 250uF capacitor is DC-blocking capacitor to prevent DC from flowing through the speaker. It's capacitance value not particularly critical. If it is too small, the low-frequency response will suffer, and the sound will sound tinny. If using a polarized cap, the + end must go to pin 5.

    The 0.05uF capacitor is to minimize the possibility that the amplifer will oscillate at a high (super-audible) frequency. It may not oscillate without it, but even if it was oscillating, it would take an oscilloscope to see it (you wouldn't hear it). If the chip is oscillating, it will get very hot to touch.

    Not shown is another anti-oscillation capacitor that should be there. That is a bypass capacitor (10uF to 220uF), + to pin 6 and - to pin 4.
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