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Class D Switching Power Amplifiers and Power D/A conversion

420W TDA8954TH Overkill? Lithium powered project
420W TDA8954TH Overkill? Lithium powered project
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Old 24th March 2019, 04:06 PM   #11
Khron is offline Khron  Finland
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Because watts = voltage ^2 / ohms

(The "current" in your equation being voltage / impedance)
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Old 24th March 2019, 04:52 PM   #12
eshamp is online now eshamp  United Kingdom
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Quote:
Originally Posted by Khron View Post
Because watts = voltage ^2 / ohms

(The "current" in your equation being voltage / impedance)
Sorry for such beginner questions!

What about briefing 2 X 24v amps?
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Old 24th March 2019, 07:52 PM   #13
eshamp is online now eshamp  United Kingdom
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Originally Posted by eshamp View Post
Sorry for such beginner questions!

What about briefing 2 X 24v amps?
So I think bridging class D amps is probably too much of a headache, so potentially a step-up converter instead. Efficiency is key in this battery powered speaker, will a step-up converter introduce too much inefficiency?
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Old 24th March 2019, 08:00 PM   #14
Khron is offline Khron  Finland
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Re: bridging, it's not necessarily complicated - most, if not all class-D amp chips contain at least one full-bridge internally.

It only depends on the board design whether you're allowed to (easily*) configure them in bridged more or not.

---
* Easily, as in, via switches or jumpers already on the board, as opposed resorting to "medieval" methods (ie. running wires and "creating" configuration jumpers yourself)
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Old 24th March 2019, 09:28 PM   #15
eshamp is online now eshamp  United Kingdom
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Cost being a factor I have narrowed it down to these four amps. One is rated for higher voltages than the other three. Am I correct in assuming the higher rated amp will have an easier time (produce less heat and less distortion at 150W) running my speaker than the other two (which will need to have a power supply close to their max)?

All are based on the IRS2092S chip.

+-30v - +-80v

+-42v - +-58v

+-30v - +-60v

+-33v - +-55v

Last edited by eshamp; 24th March 2019 at 09:44 PM.
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Old 25th March 2019, 08:40 PM   #16
strongbow60 is offline strongbow60  Sweden
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Because you need high voltage over a given resistance to have high wattage.

Se Watts/Volts/Amps/Ohms conversion calculator for a good example.

Additionally the output from the amplifier is to be considered AC voltage, so the peak voltage from the amplifier needs to be at least 1.4 times higher than the calculated value for a given wattage.

Nearly every cheap class D amplifier specifies the output power in 2 ohm, so just divide by four.

Have a look at this page for a good sounding Amp that can be used with 24 volt DC. At the end of the page is a table listing power supply range and products.

http://store3.sure-electronics.com/1...-compact-t-amp
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Old 10th April 2019, 08:46 PM   #17
eshamp is online now eshamp  United Kingdom
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Ok I understand.

I am really keen to convert a single, good PA speaker
This is because of portability and c alreadyase design/weatherproofing being done. This speaker will be carried long ways.

Pretty much all PA speakers are 8ohm. So I am restricted to an 8ohm setup.

Would a step up transformer to 40ish volts introduce too much of an efficiency loss Vs building a halfinator type speaker from scratch?

Another less preferable option is just switching the driver I'm a prebuilt speaker to 4ohm.
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Old 10th April 2019, 09:59 PM   #18
eshamp is online now eshamp  United Kingdom
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I ideally I want to get close to 100w RMS, battery powered (NiMH or LifePo4), from a single 8ohm PA speaker.
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Old 11th April 2019, 05:14 AM   #19
chermann is online now chermann  Austria
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Quote:
Originally Posted by eshamp View Post
If volts x current = watts, why is it so hard to find high wattage/low voltage class D amps?
you give yourself partly the answer
P = U*i or P = U^2 /R

as high your impdance of your speaker e.g. 8 ohms you need more "Voltage" to get more power..

RMS values/power
125W = U^2 / 8....125*8 = U^2...... SQRT(125*8) = U -- 31,6V rms on the Speakers...
so Upeak (...needed psu) 31,6 *1,4 = 44,24V


here is an excellent way how to calculate the psu
Favorite Threads and Posts in "Class D" Forum

chris
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Old 11th April 2019, 09:19 PM   #20
strongbow60 is offline strongbow60  Sweden
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Quote:
Originally Posted by eshamp View Post
...

Would a step up transformer to 40ish volts introduce too much of an efficiency loss Vs building a halfinator type speaker from scratch?


Yes, a step up converter will work. They have more or less 90% efficency, so that shouldn't be a problem. But if you buy on ebay or Ali, make sure that you read the specification with a critical eye, they are suspiciously cheap and max power can often only be used with additional cooling.
Still, you can't input more than 40V DC to a TDA8954 unit, so max output still applies.
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