+/-15v at.8A SMPS with LM3875?

jesserparker · 16th February 2008, 03:32 AM

hello,
i've come across a +/-15v switching power supply with both rails rated at 0.8a. was thinking of using this to power a lm3875 gc (possibly using two of these smps for a dual mono psu).
i would be using this to power some 89db speakers (paradigm atoms), and wondered if y'all thought that would deliver sufficient power? i may go ahead and build the thing anyhow, but was curious as to what everyone's thoughts on this were: if there was anything dangerous/important i might be overlooking; or if the damn thing just wouldn't have the chutzpah to make it worthwhile. any thoughts would be appreciated. thanks.

jesserparker · 16th February 2008, 04:35 AM

also, i should probably mention, these smps are only rated 25w. on the [very] low side of things, i know.

AndrewT · 16th February 2008, 09:24 AM

Hi,
+-15Vdc may just about give you 12Vpk at the output.
If you are using 8ohm speakers then peak current into the load can be as high as 12/8/0.35=4.3Apk on fast transients.
This peak current far exceeds the 800mA limit of the smps.
Even if you only get 10Vpk out of your amp and assume continuous maximum current is 10/8/0.5=2.5Apk that still exceeds smps capability by a factor of 3.

BTW,
12Vpk will give you 9W into 8r0.

16th February 2008, 03:32 AM	#1
jesserparker diyAudio Member Join Date: Mar 2003 Location: Ohio	+/-15v at.8A SMPS with LM3875? hello, i've come across a +/-15v switching power supply with both rails rated at 0.8a. was thinking of using this to power a lm3875 gc (possibly using two of these smps for a dual mono psu). i would be using this to power some 89db speakers (paradigm atoms), and wondered if y'all thought that would deliver sufficient power? i may go ahead and build the thing anyhow, but was curious as to what everyone's thoughts on this were: if there was anything dangerous/important i might be overlooking; or if the damn thing just wouldn't have the chutzpah to make it worthwhile. any thoughts would be appreciated. thanks.

16th February 2008, 09:24 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, +-15Vdc may just about give you 12Vpk at the output. If you are using 8ohm speakers then peak current into the load can be as high as 12/8/0.35=4.3Apk on fast transients. This peak current far exceeds the 800mA limit of the smps. Even if you only get 10Vpk out of your amp and assume continuous maximum current is 10/8/0.5=2.5Apk that still exceeds smps capability by a factor of 3. BTW, 12Vpk will give you 9W into 8r0. __________________ regards Andrew T.

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16th February 2008, 04:35 AM	#2
jesserparker diyAudio Member Join Date: Mar 2003 Location: Ohio	also, i should probably mention, these smps are only rated 25w. on the [very] low side of things, i know.

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