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Audio amplifier power supply for Class-D amplifiers

Ravindra Desai
Prodigy 250 points
Other Parts Discussed in Thread: TAS5630B

Hello,

Designing a SMPS is not easy, especially the power magnetics and moreover the cost for small quantities.

The easiest and best is a linear, unregulated power supply. However, in order to be within the safe operating voltage, I have to compromise on output power by lowering the supply voltage.

Has anyone tried giving a conventional unregulated, isolated dc supply to a DC-DC buck regulated supply to an audio amplifier?

Agreed, the input transformer will stay bulky and so will the input filter caps, but at least, it gives me a simple quick start option to power my amp NEAR the allowed voltage and not worry about voltage fluctuations.

Will the transient/ peak response suffer? What if I add large caps at the o/p of DC-DC regulator too to counter this?

Sounds redundant and crazy but gets me a regulated supply without having to get into custom magnetics design.

I appreciate any thoughts on this.

Thanks in advance and regards,

Ravindra.

  • 0
    TI__Guru**** 189399 points

    Hi, Ravindra,

    We have several power supply reference designs.

    For example, this one.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 250 points

    Hello Don,

    Thank-you for your reply. I need 48V/ 250-350Wrms AC/DC supply to power the TAS5630B. The reference design for TAS5630B is very elaborate but I need something very simple and without PFC.

    I have identified that Wurth has a 48V/250W transformer (760895751) for AC/DC applications. I am not a SMPS expert and so need help.

    Since 760895751 is available off the shelf, I am tempted to use it. Can you suggest a simplistic approach for this? I am sure there will be many who would also want it.

    Thanks and regards,

    Ravindra.

  • 0
    Prodigy 10 points

    Although the article is about 5 years old, there is some great info about exactly what you're trying to do --

    along with circuit diagrams.

    http://www.romanblack.com/gainamp.htm

  • 0 in reply to Max Wagy
    Prodigy 250 points

    Thank-you for your reply Max.

    I read the article thoroughly and it only strengthened my thoughts about switching amplifiers and switching power supplies.

    I am aborting the Class-D approach and any thoughts of a SMPS for a more classy Class-AB approach based around LM4780.

    Efficiency and heatsink are two parameters that I have to deal with. But in the process I free myself from a lot of things and it seems to me that it is well worth it:

    1. Complete through hole design for ease of manufacturing

    2. Less dependence on critical and pricy components (caps and chokes) not so easy to get locally

    3. More control over design

    4. Flexibility of configurations without much change to the BOM/ PCB

    5. At least 10 times less distortion for the same power level

    6. Quality of sound

    I will think of Class-D when my production quantity and need for much higher output increases

    Also, after giving a lot of thought, I will be using a simple un-regulated power supply using a bridge rectifier and a filter capacitor bank. The LM4780 datasheet states that a regulated power supply is not needed as the chip has excellent PSRR. So I will keep it simple to begin with and use a linear series pass regulator later sometimes to see if it does make any difference to the LF response as some say.

    Thanks again and regards,

    Ravindra.