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LM3886: Bridged Amplifier with Single Supply Voltage

Julien Leloup
Prodigy 20 points
Part Number: LM3886
Other Parts Discussed in Thread: LM2876

Hello,

I'm looking to design a bridge amplifier with the LM3886 (or LM2876) chip.

I found an application circuit in the document "AN-1192 Overture Series High Power Solutions" under chapter 5.2. Bridged Amplifier Schematic.

(link: https://www.ti.com/lit/an/snaa021b/snaa021b.pdf?ts=1692794305339&ref_url=https%253A%252F%252Fwww.google.com%252F)

I will use this schematic as an orientation since the input signal should also be unbalanced in my design.

My question here is: Can I build this bridged circuit as well with a single power supply?

I've found a document in the LM3886 datasheet showing an application for this, but not as a bridge (page: 6, figure 3.).

I'm also wondering what the transistor Q1 does here?

Best regards,

Julien Leloup

  • 0
    TI__Mastermind 35520 points

    Hi Julien

       The Q1 is try to created a suitable DC bias at Input side.

       To using single power supply, there's two things we need to do:

       1. To add a suitable DC bias at input side. Because the input audio signal would be AC signal, has both positive and negative voltage. By using single supply, the device won't able to handle the negative voltage. The DC bias would add into the input signal, to make sure all of them above 0V.

       2. Need a very large DC block capacitor at Output side to remove all the DC signal. Because the Speaker can't accept DC voltage, may got damage. Since you add a DC into the input, you must remove it at output. This is the 4700uF you could find in datasheet page6, figure 3.

       So in the bridged circuit application guide, they didn't do any of this two points, so they are all need dual power supply.

  • 0 in reply to Shadow He
    Prodigy 20 points

    Thanks for your quick reply!

    Is it possible to do a bridged circuit with a single power supply without using the DC block capacitor at the output, since it should balance itself out with the bridge?

  • 0 in reply to Julien Leloup
    TI__Mastermind 35520 points

    Hi Julien

        Yes, it is possible. Only the circuit would complex.

        If the single power supply and bridge circuit is your most important requirement, maybe you could consider Class-D amp, could make the circuit simpler.

  • 0 in reply to Shadow He
    Prodigy 20 points

    Thanks for your reply!

    They are indeed important requirements, but it's also important for me to use the LM3886 and not any class-D chip.

  • 0 in reply to Julien Leloup
    TI__Mastermind 35520 points

    Hi Julien

       I see. Then we could have a try.