24 volt DC chip amp

Philfr · 16th December 2012, 04:36 PM

Hi all,
First, I'am writing from France and my english was not very good

, sorry.
I'am looking for a chip amp working on 24 v DC (with two 12 v gel battery)..
I saw the LM1875, cause I want a minimalist schematic and no pcb.
Thank you for your comments.
Phil.

Mooly · 16th December 2012, 05:18 PM

A couple of thoughts...

Some chips (or discrete amplifiers too) react badly when the supplies don't rise and fall together. With batteries and a switch that could happen. You might also need a speaker relay delay.

Gel batteries are great put have huge energy reserves so make sure you fuse each one directly at the terminals of the battery.

Philfr · 16th December 2012, 06:22 PM

Hi Mooly,
Yes I think add a softstart and speaker protection..
For battery, maybe a big capacitor (1 Farad) solve the problem ?
I have not found articles about battery supply for amp, except on car audio with voltage elevator.

Mooly · 16th December 2012, 06:26 PM

Not sure the big cap is a good idea, not using switches... charge current and all that !

It should be possible to come up with a simple switched rail design perhaps using low Rds FET's (one for each rail) as the switch elements and control both these from a common on/off signal.

AndrewT · 16th December 2012, 06:26 PM

Soft start is for starting a mains transformer.
If you power by battery you don't have a mains transformer. You don't need a soft start.

Philfr · 16th December 2012, 06:55 PM

@ Mooly,
what is "low Rds FET's" ?
Thank's in advance.
@ Andrew,
indeed

Mooly · 17th December 2012, 03:52 PM

Simply put they are FET's that have a low on resistance and so don't heat up when used as a switch. So no heatsink required when used as a switch.

Philfr · 17th December 2012, 04:34 PM

Hi Mooly,
Thank's, I see clearer..
Maybe TDA7294 was better in my case ?
The goal is to drive a subwoofer until 200 hz.

Mooly · 17th December 2012, 04:34 PM

Something like this. R1 and R3 are the "load" or amplifier. R5 would have a single switch in series with it. Closed for on and open for off. The FET's run cold.

(The IRFP9240 isn't the most suitable but just chosen because its in the standard spice parts library)

Mooly · 17th December 2012, 04:37 PM

Quote:

Originally Posted by Philfr

Hi Mooly,
Thank's, I see clearer..
Maybe TDA7294 was better in my case ?
The goal is to drive a subwoofer until 200 hz.

Any power amp chip will work down to as low a frequency as you want. Will the TDA 7294 work at that voltage... I'd have to check the data sheets.

16th December 2012, 04:36 PM	#1
Philfr diyAudio Member Join Date: Dec 2012	24 volt DC chip amp Hi all, First, I'am writing from France and my english was not very good , sorry. I'am looking for a chip amp working on 24 v DC (with two 12 v gel battery).. I saw the LM1875, cause I want a minimalist schematic and no pcb. Thank you for your comments. Phil.

16th December 2012, 05:18 PM	#2
Mooly diyAudio Moderator Join Date: Sep 2007	A couple of thoughts... Some chips (or discrete amplifiers too) react badly when the supplies don't rise and fall together. With batteries and a switch that could happen. You might also need a speaker relay delay. Gel batteries are great put have huge energy reserves so make sure you fuse each one directly at the terminals of the battery. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

16th December 2012, 06:26 PM	#4
Mooly diyAudio Moderator Join Date: Sep 2007	Not sure the big cap is a good idea, not using switches... charge current and all that ! It should be possible to come up with a simple switched rail design perhaps using low Rds FET's (one for each rail) as the switch elements and control both these from a common on/off signal. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

17th December 2012, 03:52 PM	#7
Mooly diyAudio Moderator Join Date: Sep 2007	Simply put they are FET's that have a low on resistance and so don't heat up when used as a switch. So no heatsink required when used as a switch. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

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16th December 2012, 06:22 PM	#3
Philfr diyAudio Member Join Date: Dec 2012	Hi Mooly, Yes I think add a softstart and speaker protection.. For battery, maybe a big capacitor (1 Farad) solve the problem ? I have not found articles about battery supply for amp, except on car audio with voltage elevator.

16th December 2012, 06:26 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Soft start is for starting a mains transformer. If you power by battery you don't have a mains transformer. You don't need a soft start.

16th December 2012, 06:55 PM	#6
Philfr diyAudio Member Join Date: Dec 2012	@ Mooly, what is "low Rds FET's" ? Thank's in advance. @ Andrew, indeed

17th December 2012, 04:34 PM	#8
Philfr diyAudio Member Join Date: Dec 2012	Hi Mooly, Thank's, I see clearer.. Maybe TDA7294 was better in my case ? The goal is to drive a subwoofer until 200 hz.

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