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Class D Switching Power Amplifiers and Power D/A conversion

80%+ efficiency amp running @12V single rail with 400...500W @ 8 ohms
80%+ efficiency amp running @12V single rail with 400...500W @ 8 ohms
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Old 3rd August 2013, 06:15 PM   #1
meko is offline meko  Denmark
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Default 80%+ efficiency amp running @12V single rail with 400...500W @ 8 ohms

Hello everyone,

I have a slight problem: I need a high-efficiency (class D style) amplifier that has to be powered from a 12V battery system, so it should be running with 9...15V input voltage.
Efficiency should be in the 80% range.
It has to output 400 or 500 WRMS into an 8 (eight!) ohm load without problems.
It has to be reliable. I can't have the amp break down. I originally wanted to get a premium car audio amplifier for this application, but the only ones that I can consider are the larger digital monoblocks that are totally tailored towards very low impedances.
When I find an amp that can deliver ~1000WRMS into 4 ohms, that amp is a monster that can deliver 2KW into 2Ohms and sometimes even more.
I am afraid that the power supplies are so large that the amp will be draining a lot of battery when I drive it at "only" 400 or 500W. At least more current than an amp that is designed to deliver half a KW.
Is that assumption correct?
I found the ebay-versions of that international rectifier evaluation board (I think "IRAUDAMP7S") that seems to do the job, but I am not too confident that this is reliable enough. And a SMPS to supply the bipolar supply voltages from 12V is going to be another thing that I'll have to get from china and I will not know how reliable that is either.
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What is your suggestion? Is a "digital monoblock" car amp really as bad as I think for battery life when driven at low output? Would I be better off using a class A/B car audio amp?
Thanks!
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Old 3rd August 2013, 08:13 PM   #2
Phaedras is offline Phaedras  Denmark
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Check out this amp.. Its a class d monoblock and will probably do what you want..

DB1.2 - Class-D Monoblock - Bass Face Car Audio
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Old 3rd August 2013, 08:34 PM   #3
geraldfryjr is offline geraldfryjr  United States
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The power supply requirements for ClassAB amp's also apply to ClassD amp's.

In order to get 1000watts into 4 ohms will require 89.44v power supply rails, Both positive and negative rails.

The same apply's to 500 watts into 8 ohms.

This not include any output device or power supply diode voltage drops.

FWIW

jer

Last edited by geraldfryjr; 3rd August 2013 at 08:38 PM.
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Old 3rd August 2013, 09:34 PM   #4
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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To deliver 1kW into 4R a beefy switch mode power supply delivering + and - 90volts. It is not practical for a vehicle unless you have an alternator that will deliver in excess of 100Amps and wired up with 10mm tails! Assuming that is what you require it for that is.
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Old 3rd August 2013, 09:46 PM   #5
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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I wouldn't trust this amp at 500Watts for long. The design is good, Vishay (was I/R) but limiting performance. I would increase the output Fets to achieve what you are looking for. Maybe double up in parallel to achieve 1kW in bridge mode..
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Old 4th August 2013, 02:14 AM   #6
meko is offline meko  Denmark
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Thanks for the help so far! A battery array with sufficient current capabilities is of course going to be a part of the system. several hundred amps is no problem at all. However, I want the amp to run at very high efficiency even if I drive the speaker with only 70 watts. How will a class D monoblock that is rated at 1000W @ 4ohm behave in that situation?

I guess I don't trust the IR amp either. I think modifying it is not an option for me right now.

Phaedras, thanks! That looks like a nice amp and it has a very compact form factor. Great. And it is even affordable. Have you got any experience with these?
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Old 4th August 2013, 04:25 AM   #7
DUG is offline DUG  Canada
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If you are going to use multiple 12V batteries then why not 6 of them in series for a +/- 36V supply and use something like a TDA8954 and get 260-280W (0.5%THD or 340-350W 10%THD) 8R at about 90% efficiency?

Or a few more with a higher power class D IC?
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Old 4th August 2013, 04:35 AM   #8
geraldfryjr is offline geraldfryjr  United States
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It is not uncommon for a Class D amp to have 90% efficiency or better.

FET's with the lowest Rdson will give you the best results of high efficiency.

Having a very short dead time is also critical to increasing the efficiency as long as you don't have any shoot through current through the output devices or else they will fail with a very loud bang and flying peices.

Take a look at this thread as projects such as this are already on going,

ucd 25 watts to 1200 watts using 2 mosfets

Good Luck!!

jer

P.S. The best thing to do is build a low voltage one and learn how they work before messing with one that has 90v rails at over 5 to 10 amps each.

Last edited by geraldfryjr; 4th August 2013 at 05:03 AM.
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Old 4th August 2013, 09:42 AM   #9
meko is offline meko  Denmark
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Quote:
Originally Posted by DUG View Post
If you are going to use multiple 12V batteries then why not 6 of them in series for a +/- 36V supply and use something like a TDA8954 and get 260-280W (0.5%THD or 340-350W 10%THD) 8R at about 90% efficiency?

Or a few more with a higher power class D IC?
the idea is in fact very tempting and I was thinking about doing it like that for some time. the tda8954 seems nice but is hooking it up directly to batteries really an option? when using 6 or 8 12V batteries in series, they will very likely be at slightly different voltages each. so there would be an asymmetry in the bipolar supply to the chip. will that not cause failure? would I need voltage regulators? do you know a class d chip that can handle +-48V and put out 400W @8R at low THD?

Last edited by meko; 4th August 2013 at 09:59 AM.
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Old 4th August 2013, 01:00 PM   #10
Saturnus is offline Saturnus  Denmark
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Quote:
Originally Posted by meko View Post
the idea is in fact very tempting and I was thinking about doing it like that for some time. the tda8954 seems nice but is hooking it up directly to batteries really an option? when using 6 or 8 12V batteries in series, they will very likely be at slightly different voltages each. so there would be an asymmetry in the bipolar supply to the chip. will that not cause failure? would I need voltage regulators? do you know a class d chip that can handle +-48V and put out 400W @8R at low THD?
No. Batteries in series will not show different voltage potential on the 2 rails unless they are completely separated or subjected to different loads on the two rails but even then the rails will quickly align themselves.

I know the Bassface amp suggested above, and was the first to propose the use of that or similar low cost simple class D amps as they have very good efficiency, probably most in the 80% region or better in their limited frequency range, and they run directly on 12V which makes integration in a portable system much easier as you will probably have a lot of other things that run on 12V. The other point of using them is that the since sound quality in a regular hi-fi sense is basically not needed, or you could even argue that it would be non-sense to even call it that, for a bass frequency only amplifier. The only requirement is that it can reliably output sufficient power into the loads presented to it, and that it has integrated active filters that makes it easy to incorporate. In that sense, I, and indeed most people who have heard it, can testify that the Bassface amp or other similar amps does in fact do that.
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