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I have a power supply(DC) rated ~7.2A @ 34.5v. I am looking forward to drive an amplifier rated ~6A @ 34v(upper limit. actually 15 - 34VDC).

So my question is about the difference between supply and amp (0.5v excess). What are the chances that the difference(0.5v) is not tolerated and the amp is fried?

For me 0.5v difference is just ~1.5% higher then rated voltage, so assuming should be tolerable. But, since there is no datasheet available I could not confirm the same.

I could see similar question but for lower voltage like 4.5 vs 5 or 5 vs 6 or max was 12 vs 14.4 where the difference % of voltage is much higher then my scenario, so did not help much.

So, I would like your help to learn about your experience on similar scenario, you may have seen earlier. Or perhaps a theory for a possible outcome.

Extra Info:

  • Amp board: TDA7498 based chip (TDA7498 2*100w amp @ ebay)
  • Power supply: Salvaged from a broken Philips Sub-woofer
  • Power supply delivers exactly 34.5v under no load condition, I could not test it under load until now.

Options received until now:

  • Use diode to drop some volts(will research on the spec)
  • Do nothing, use as it is (last resort)
  • I have seen similar chip being rated for higher voltages as well (15-36v), so assuming chip may tolerate the difference. Supports do nothing conclusion. Ref TDA7498E 2*160 amp @ ebay

Final

  • Added 2 6a diodes to drop around 1.2 volt (actual result -1.5v, net 33v)
  • Attached 2" of heat sink to control heat (looks ok, not very hot under load)
  • Added few caps(~3000uf) to stabilize voltage (was dropping to 15v under load)

Result is great, amp drives great. Thank you guys for the assistance.

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  • \$\begingroup\$ It might be fine, it might not be. You'd be running the device out of spec. You could put a diode in series with the supply to drop it a little if you're concerned. \$\endgroup\$
    – Colin
    Nov 16, 2017 at 8:29
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    \$\begingroup\$ It is highly unlikely that an extra 0.5V is going to cause damage to an amplifier. Can you measure the voltage of the power supply, especially under load (6A)? It may be that your power supply does output exactly 34.5V anyway. \$\endgroup\$
    – Steve G
    Nov 16, 2017 at 9:19
  • \$\begingroup\$ IF the amplifier is IC-based, that IC will have an "Absolute Max" voltage rating in its datasheet. Don't exceed that. \$\endgroup\$ Nov 16, 2017 at 9:40
  • \$\begingroup\$ Hi guys, I have added more details. See if this helps. \$\endgroup\$
    – pushpraj
    Nov 16, 2017 at 10:53
  • \$\begingroup\$ Without a data sheet you are doing the equivalent of designing by prayers i.e. you aren't designing. Don't use parts without data sheets period. \$\endgroup\$
    – Andy aka
    Nov 16, 2017 at 12:57

2 Answers 2

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To expand on the comment from Colin-s, a simple silicon rectifier diode drops about 0.6V when forward biased. This would drop your 34.5V down to 33.9V. Just get one that's rated for the current you need.

As a handy side-effect, if you put it on the power input of the amplifier, it also protects against somebody connecting up the power supply the wrong way round.

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    \$\begingroup\$ Be aware, if you are pulling 6A then the diode will be dissipating 0.6 * 6 = 3.6 watts. Look for something in a TO220 or larger package and put a reasonable heatsink on it. \$\endgroup\$
    – Colin
    Nov 16, 2017 at 11:11
  • \$\begingroup\$ Thank you for the explanation. Big thanks to @Colin__s for sharing additional concern about heat from the loss. I managed to find a few 6A diodes. I'll give this a try today. \$\endgroup\$
    – pushpraj
    Nov 17, 2017 at 1:09
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The TDA7498 has an absolute maximum rating on the power supply of 45V, nothing else on that board is likely to be affected by a .5V increase in voltage. You should be ok as is.

You should not use the device at its absolute maximum rating you need to leave some room for unwanted excursions of the power supply voltage.

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  • \$\begingroup\$ I appreciate your efforts and agree with your idea to allow a room for any fluctuation. Though, I doubt as the supply is pretty much regulated, but who knows. Secondly, it is unlikely that the board may affect with a slight increase in voltage. But, chip rating of 45v may not have significant impact here as most of the visible caps appears rated for 35v, so unlikely that it is going to tolerate much over 35v. \$\endgroup\$
    – pushpraj
    Nov 17, 2017 at 1:14

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