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how to specify power supply requirements to drive amplifier chips?

Mark Thompson2
Intellectual 610 points
Other Parts Discussed in Thread: PMP10215

Hi there,

I'll start by saying I don't know much about power supply design.  I've not had to understand the power supply requirements to drive amplifiers before; now I need to.  My colleague has acquired some 2ch class-D amplifiers that provide 2 x 25W output power (for a nominal load impedance of 8-Ohm).  The amps are ~ 87% efficient at these conditions, when driven from a 20V supply.  Can you help me understand how I use this information about the amplifier chip to determine my power supply requirements to safely drive this amplifier?  I then need to understand how I can design a power supply that can power multiples of these amplifiers.

Any assistance, and design guidance, you can provide would be amazing!

Many thanks!

  • 0
    TI__Mastermind 35895 points

    Hi Mark,

    Although you provided us with a competitor part in the link, I will help you understand your power supply needs and hopefully you will start a link in the power forum for power supply design help.

    You have 2x25W=50W total output power.  At 87% efficiency, 50W/0.87=57.5W for the power supply power.  The stated conditions are 20Vdc and at 57.5W of power, the minimum current rating needs to be 57.5W/20V=2.9A.  If you have multiples, multiply the current by the number of amplifiers.

  • 0 in reply to Gregg Scott
    Intellectual 610 points

    Thank you Gregg.  That clarification helps.

    One last thing though, can you assist me in developing a power supply to drive up to 10 of these chips.  I much prefer working with TI!  (other amps were acquired by a colleague, not me...)

  • 0 in reply to Mark Thompson2
    TI__Genius 9180 points

    Hello Mark,

    I would encourage you to start a thread in power forum, as they are expert on power supply design.

    Dylan

  • 0 in reply to Dylan Yao
    Intellectual 610 points

    I did!  Well, at least I thought I did.  I followed the forum links until I got to the Power thread, and here I am.  This is the Power Management forum isn't it?

  • 0 in reply to Mark Thompson2
    TI__Genius 9180 points

    Mark,

    I see..i will assign it to a power design support team.


    Dylan

  • 0 in reply to Dylan Yao
    TI__Guru 59435 points

    Hello Mark,

    Gregg mentioned already that you would need a power supply of 20V/2.9A for driving 2 25W power amplifiers.

    Now, you asked for a power supply for 10 of these, so I would need to understand at least the following information to help proposing a converter:

    1. Which input voltage range is available in your system to create the +20V?

    2. Do you want to drive 10 Amplifiers with 25W or 10 systems with 2 amplifiers so 20 amplifiers in total?

    3. The voltage on the amplifiers shall be 20V on the high side and 0V on the low side, right? I am asking because amplifiers can often as well be supplied by +/- V instead of +V / 0V.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Intellectual 610 points

    Hi Brigitte, thanks so much for your response!

    1. We are working on 240V, 10 A, supply here in Australia.

    2.  I wish to drive 10 x 2ch amplifiers.  So all up, 20 x 25W channels.

    3. 0 V to +20 V.

    Thanks so much.  I look forward to working with you to create a supply for this!

  • 0 in reply to Mark Thompson2
    TI__Guru 59435 points

    Hello Mark,

    So your input voltage is expected to be the 240V AC mains, right? So we are speaking about 500W output power.

    Do you plan to use a plug-in power converter to get DC voltage and if yes, what is the output voltage of this one. If not, the solution will be similar to this one, I expect: https://www.ti.com/tool/PMP5500

    As far as I know, you need power factor correction at this power level as well as isolation, but you need to clarify your use case in detail.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Intellectual 610 points

    correct.  240V AC Mains as input to the power supply.  The amplifier datasheet quotes 87% efficiency, therefore, each 50 W amplifier requires at least  50 W / 0.87 = 57.5W for the power supply power.

    I would like assistance designing a solution similar to the reference design you noted (PMP5500); PFC and isolation is of course important, however my design requires different output DC voltages.

    I need to achieve the following DC Voltage outputs:

    1 x 5V DC output capable of providing at least 1.5 A. (basically just to power a DSP peripheral.  If this is too difficult to include I'll just provide a separate supply for this).

    1 x 20 V DC output (can split into 2 x outputs if easier, cheaper, safer...) capable of delivering a minimum of 2.9 A to each of my 10 x amplifier chips.  Therefore a minimum of 29 A to be shared equally between the 10 x amplifiers.

    Each amplifier will be driving 2 x speakers to create a 20 x speaker array.  So the current and voltage requirements for the amplifiers assumes normal operation, it would be nice to know that the power supply can cater for short (~ 10 ms) peaks/spikes that may be between 5 A or 10 A at each amplifier.  

    Noise into each amplifier from the power supply needs to be managed.  Hence my original query about a linear supply that can achieve my requirements, but apparently we may be able to achieve similar functionality with a SMPS design?!  Happy to be lead by you on that.

    Many thanks.

    Mark

  • 0 in reply to Mark Thompson2
    TI__Guru 59435 points

    Hello Mark,

    Let me try to find a reference design that you could use as starting point.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Intellectual 610 points

    Many thanks Brigitte!  Thank you for your support!

  • 0 in reply to Mark Thompson2
    TI__Guru 59435 points

    Hello Mark,

    Until I get feedback, you might have a look at the reference design I already sent you and check out the details to get some more information on what is needed for such a supply.

    In addition, we have a lot technical material on power supplies online, e.g. here: https://www.ti.com/power-management/power-supply-design-seminars/resources.html?DCMP=pwr-psds-archive&HQS=pwr-psds-archive-psds

    If you need to dig into power supplies and are really not experienced at all, I recommend these short videos on different topics: https://training.ti.com/experimental-power-electronics-curriculum-and-reference

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Intellectual 610 points

    Thank you for the URL with the electronics videos.  That will certainly be helpful along the way!

    I will await feedback regarding my specific design requirements.

    Would either of these suffice as reference designs?  Or are they not really suited to audio systems design?

    https://www.ti.com/tool/TIDA-01494

    and

    https://www.ti.com/tool/TIDA-010015

    Regards,

    Mark

  • 0 in reply to Mark Thompson2
    TI__Guru 59435 points

    Hello Mark,

    I do not expect that these are the right solutions for your application. In the meantime I found the right person to ask with a lot more experience on powering audio amplifiers. Please have a look at this training material: https://training.ti.com/power-solutions-class-d-audio-amps

    If you prefer to read instead of listening, check out the white paper on this site.

    Here you can find a reference design for audio amplifers: https://www.ti.com/tool/PMP10215

    According to the expert the power should be enough for your application after you changed the secondary side from 36V to 20V. Normally this should bring you an output current of 10 Arms and around 30 Apk. I expect that this is a good starting point as most probable you will not need the theoretically calculated 29A for a longer period of time.

    Thank you for this interesting application. I did learn as well a lot and will dig more into its details myself :-)

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Intellectual 610 points

    Hi Brigitte,

    Can you explain what aspects of those 2 reference designs I sent you make them unsuitable for my application?  I just want to understand a little more why.

    Are you suggesting that my solution is to modify the PMP10215 design?  If so, can TI provide me some product recommendations that I can use to achieve this modification?  Is it possible to achieve 20 V DC output and at least 20 Arms?  If not, what else can I change to achieve this?

    Thank you again for your support!

  • 0 in reply to Mark Thompson2
    TI__Guru 59435 points

    Hello Mark,

    Please go to the website which gives you the white paper on power solutions for audio amplifier. I think your questions are answered if you read through this white paper and it gives you a lot more information about power supplies for audio amplifiers.

    The suggestion is to modify PMP10215 (please check out the white paper which should help to do so) and normally the power should then be enough for your application as explained above.

    Best regards,
    Brigitte

  • +1 in reply to Brigitte
    TI__Guru 59435 points

    Hello Mark,

    Some additional information how to get the converter or PMP10215 updated for your design:

    The transformer needs to be update with the right turns ratio, need to update the diodes for higher current, output caps with lower voltage rating might be ok, but you might need some higher values due to the higher current, the loop needs to be re-calculated.

    If you are using components with the same form factor, you could even use the same PCB as the PFC already seem to fit the needs of your system (normally the max power is not needed for long and as you can see on the schematic the design can deliver up to 840W for a short period of time).

    Please be careful as you are working with this design at high voltage. This means normally special training is needed as it is dangerous to work on such voltages. I do have experience with power designs, but I would not work on such a design without discussing it in detail with an expert.

    Danger, High Voltage, 240Vac, 400Vdc

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Intellectual 610 points

    Many thanks, Brigitte!  I appreciate your support.  Kind regards!