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Is it possible to get dual power supply from single power supply?

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Ziddik

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Hii, i have bought a 12V 30A single power supply for powering an audio amplifier. But the problem here is my subwoofer amplifier needs dual power supply, so i need a +12V-0V- -12V at 10 amps to power the circuit, is there any way i can make it possible with single line power supply?
 

dknguyen

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Because the methods available that I know of don't have low enough impedance or high enough capacity to support that level of current. If there is a method I'd love to hear about it too but I don't think one exists.
 

unclejed613

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the correct way to do that requires a second 12V supply. you would have two supplies, "a" and "b". the positive of supply "b" connects to the negative of supply "a". that connection becomes ground, and the negative of supply "b" is the -12V rail, and the positive of supply "a" is the +12V rail. if these supplies are in chassis boxes, and have a ground pin on their AC line cords, you want to make sure the chassis box is isolated from the 12V supply or you could end up with a short across the "b" supply when the supplies are plugged into the wall outlet.

another method would be to run a DC-DC converter that outputs [email protected] when driven from the +12V rail. since the DC-DC converter is running off the same supply used for the +12V supply, you will be drawing about 22A from the power supply when each rail is loaded to 10A.
 

audioguru

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If the amplifier has a single output then with a 24V total supply its max output swing might be 22V p-p which is only 7.78V RMS. Then the power into 4 ohms is only 15W. If the amplifier has a bridged output then the output power is only 60.5W and the heating is about 50W so the total power from the power supply is 110.5W. Then the max power supply current is only 110.5W/24V= 4.6A. Are there two 4 ohm subwoofers and two bridged amplifiers?
 

Ziddik

Member
.. if these supplies are in chassis boxes, and have a ground pin on their AC line cords, you want to make sure the chassis box is isolated from the 12V supply or you could end up with a short across the "b" supply when the supplies are plugged into the wall outlet.



another method would be to run a DC-DC converter that outputs [email protected] when driven from the +12V rail. since the DC-DC converter is running off the same supply used for the +12V supply, you will be drawing about 22A from the power supply when each rail is loaded to 10A.


Hi unclejed, the dc-dc converter you mentioned may be helpful, i am looking for one online and found this https://www.amazon.in/DC-Converter-...scsubtag=8f2069ce-2adc-4b53-a703-13088760586a but sadly it can only output 3A-5A, my subwoofer needs atleast 10A, is there any similar circuit that you know?, my powersupply is a SMPS, and yes i was mistakenly bought it because i thought it had dual supply out, but the Ground sign of it was for earthing on the wall, not the 0v line. Here is a photo of it 15387871509041854968041.jpg1538787197851780553873.jpg
 

Ziddik

Member
If the amplifier has a single output then with a 24V total supply its max output swing might be 22V p-p which is only 7.78V RMS. Then the power into 4 ohms is only 15W. If the amplifier has a bridged output then the output power is only 60.5W and the heating is about 50W so the total power from the power supply is 110.5W. Then the max power supply current is only 110.5W/24V= 4.6A. Are there two 4 ohm subwoofers and two bridged amplifiers?
Hi guru, it's a 4.1 sound system that i want design but the subwoofer circuit board needs 27-0-27V so i bought this (attached below) to boost 12V to 27V , i want use LA4440 for 4 channels because these ics will work from single supply, and a MOSFET Amp board for subwoofer out but that needs the dual supply, the board's output capacity is printed as 400 Watts, do you think 2 MOSFETs can provide 400 watts out from just 27V 10 Amps supply?​
 

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audioguru

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Didn't you see my post? With only 24V it is almost impossible for an amplifier to use 10A. If the amplifier is bridged for most power and the speaker is 4 ohms then the speaker gets 60.5W and heating is about 50W for a total power from the power supply of 110.5W. Then the max current is only110.5w/24V= 4.6A, not 10A.
 

audioguru

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Before the subwoofer amplifier needed plus and minus 12V but now it needs plus and minus 27V.
The 54V Mosfet amplifier is rated at 400 phoney Whats when it is clipping like crazy, which is about 325 real Watts with reasonably low distortion if the speaker is 4 ohms. The heating will be about 215W so the power supply must produce a current of (325W + 215W)/54V= 10A.
 

Ziddik

Member
Before the subwoofer amplifier needed plus and minus 12V but now it needs plus and minus 27V.
The 54V Mosfet amplifier is rated at 400 phoney Whats when it is clipping like crazy, which is about 325 real Watts with reasonably low distortion if the speaker is 4 ohms. The heating will be about 215W so the power supply must produce a current of (325W + 215W)/54V= 10A.
215 W heating? That's a lot of efficiency losing right there, i need an energy efficient sound system with clean output sound.
 

audioguru

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A class-AB amplifier heats the most when its output power is at about 60% of its power when it begins clipping. With lower levels its heating is low.
There are some very efficient class-D amplifier ICs available from Texas Instruments.
 

Nigel Goodwin

Super Moderator
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Before the subwoofer amplifier needed plus and minus 12V but now it needs plus and minus 27V.
The 54V Mosfet amplifier is rated at 400 phoney Whats when it is clipping like crazy, which is about 325 real Watts with reasonably low distortion if the speaker is 4 ohms. The heating will be about 215W so the power supply must produce a current of (325W + 215W)/54V= 10A.
I'm a litle confused by your figures?, for a single ended amplifier off a 54V supply rail, I make it as less than 75W in to 4 ohms, and probably a fair bit less as it's MOSFET, and they don't do well getting close to the supply rails. Assuming it's a bridged amplifier?, then you're looking at four times the power, so under 300W in to 4 ohms.

As for the OP, BUY the correct voltage PSU - it's a really silly idea buying totally the wrong one, and then trying to add things on to make it work. You say you want 'efficient' - you've completely blown that in the first place by not buying the correct supply.
 

audioguru

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New terms: phoney watts and fake news. Learn something new every day.
I say that phoney watts are Whats.
A car radio that produces 15 real low distortion Watts per channel into 4 ohm speakers has 4 channels so its total real output power is 60 Watts. But they are advertised at 200 to 250 Whats when clipping like crazy. Some amplifier ICs are rated in EIAJ Watts which has a squarewave input so that the output is not linear, it switches high and low.
A squarewave output has the same amount of power in its distortion harmonics as the fundamental frequency so the power number is doubled.

Nigel, some new Mosfet amplifiers produce less voltage loss than amplifiers with bipolar transistors. The TDA8594 Mosfets quad bridged car radio amplifier IC is rated at 22W per channel with 0.5% distortion into 4 ohm speakers. Then its output swing is 9.4V RMS and its peak-to-peak swing is 26.6V. But its supply is 14.4V x 2= 28.8V so its output voltage loss is only 28.8V - 26.6V= 2.2V. Applying that loss to the Mosfets bridged amplifier that has a 54V supply results in 333W with 0.5% distortion into 4 ohms. The voltage loss at such a high power is probably more than 2.2V so the output is probably "only" 300W.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Applying that loss to the Mosfets bridged amplifier that has a 54V supply results in 333W with 0.5% distortion into 4 ohms. The voltage loss at such a high power is probably more than 2.2V so the output is probably "only" 300W.
It's a bit optimistic assuming a high powered amplifier will have anywhere near the losses of a specially designed small one, plus you're ignoring the drop of the supply voltage as well.
 
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