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Old 15th December 2005, 04:57 PM   #1
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Exclamation SMPS - Buck converter - HOW !?

Hi people !

I want to design a HUGE power amp , 4ch, 300W RMS each one, bridgeable... Buts as I need 500VA PSU for each channel, I'll need a 2000VA PSU

But, there's no space enought to put a commom transformer inside the case, and even if it's outside, I think it's impratical...

So, I need a swithing power supply that takes 127 or 220V and convert it to + - 50V.

Look, this is how the supply should work, I think...

http://schmidt-walter.fbe.fh-darmsta...lfe_e.html#top


Any ideas?
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Old 15th December 2005, 06:57 PM   #2
subwo1 is offline subwo1  United States
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Hi, one very bad thing about that topology is that it is not isolated from the power line. The user becomes at risk of electric shock. I'd say you want to use switching transformers. Then at least you can use two isolated windings to obtain +/-50v from each transformer.
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Old 15th December 2005, 07:46 PM   #3
poobah is offline poobah  United States
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Nando,

Here is one of the best Application Notes for switchmode design.

Linear Technology's AN19:

http://www.linear.com/pc/downloadDoc...61,P1266,D4176
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Old 16th December 2005, 05:38 PM   #4
Eva is offline Eva  Spain
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nando:

You are going to need much more than just a theoretical buck converter taken straight from some text book in order to match your goals. Read further into this forum, there are several threads dealing with off-line SMPS.
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Old 16th December 2005, 05:49 PM   #5
poobah is offline poobah  United States
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Subwo & Eva, make very good points,

You should have line isolation if possible, by the time you purchase such a large transformer for isolation... why not simply derive your B+ from a standard bridge rectifier / filter?

It will be very difficult to find/build the ferrite transformers required for a good buck design in that power range.
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Old 16th December 2005, 06:59 PM   #6
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Yes... Realy not easy, but I can build one supply for each channel, then it will be more easy...

I was looking PC supplys, that is of course, an offline buck converter, and the supply use 400v fast switching transistors, look:

http://www.ortodoxism.ro/datasheets/mospec/MJE13007.pdf

One ordinary PC supply can deliver about 200W, just with TWO of that transistors, ONE Mosfet (30v 0,022Ohms 40A) and a small transformer...

That's why I'm learning about switching buck converters, I think it's a real good solution, and the more important, it's REGULATED...

When we use the ordinary LARGE transformer, the voltage falls down very easily when we turn the bass and volume up, then the amplifier can't deliver the rated power...

For example, I made a stereo set for the computer of one friend, using two TDA2050, that each one deliver 30W @ 4Ohms @ 22.5v THD < 0,5%... Then I bought 18+18 4A transformer, after retification deliverier 27+27V... When the music was playing loud, the voltage falled down to 19+19... OK, but when stand by returned to 27+27 that BURNED the TDA after a while... Then I bought the 15+15 transformer that deliveried 22.5+22.5 in STAND BY mode, and when loud, 14+14v

Then, I rated the amplifier 19+19 W RMS.... Because:

Amplifier efficience is

22.5v + 22.5v = 45v
(45v / 2*1.41)/ 8 (load) = 32W RMS (100% efficience)

Ok, as the Datasheet says, the amplifier in these conditions above, can deliver 25W, so:

32 --- 100
25 --- X

X = 78,125 % of efficience.

Then

14+14v = 28v
(28v / 2*1.41)/ R (load) - 22% (78% eficience) = 18,5W RMS...

If I used the swithing buck converter:

22.5 + 22.5 = 45v
(45v / 2*1.41)/ 4 (load) = 64W - 22% (78% efficience) = 50W RMS

That power they call "music" power, that is the power if the supply can deliver continuous voltage, without any slow down...

And that's the difference between normal PSU (LARGE transformer with common retifier) and the SMPS Buck converter...




Waiting for opinions !
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Old 16th December 2005, 07:00 PM   #7
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Yes... Realy not easy, but I can build one supply for each channel, then it will be more easy...

I was looking PC supplys, that is of course, an offline buck converter, and the supply use 400v fast switching transistors, look:

http://www.ortodoxism.ro/datasheets/mospec/MJE13007.pdf

One ordinary PC supply can deliver about 200W, just with TWO of that transistors, ONE Mosfet (30v 0,022Ohms 40A) and a small transformer...

That's why I'm learning about switching buck converters, I think it's a real good solution, and the more important, it's REGULATED...

When we use the ordinary LARGE transformer, the voltage falls down very easily when we turn the bass and volume up, then the amplifier can't deliver the rated power...

For example, I made a stereo set for the computer of one friend, using two TDA2050, that each one deliver 30W @ 4Ohms @ 22.5v THD < 0,5%... Then I bought 18+18 4A transformer, after retification deliverier 27+27V... When the music was playing loud, the voltage falled down to 19+19... OK, but when stand by returned to 27+27 that BURNED the TDA after a while... Then I bought the 15+15 transformer that deliveried 22.5+22.5 in STAND BY mode, and when loud, 14+14v

Then, I rated the amplifier 19+19 W RMS.... Because:

Amplifier efficience is

22.5v + 22.5v = 45v
(45v / 2*1.41)/ 8 (load) = 32W RMS (100% efficience)

Ok, as the Datasheet says, the amplifier in these conditions above, can deliver 25W, so:

32 --- 100
25 --- X

X = 78,125 % of efficience.

Then

14+14v = 28v
(28v / 2*1.41)/ R (load) - 22% (78% eficience) = 18,5W RMS...

If I used the swithing buck converter:

22.5 + 22.5 = 45v
(45v / 2*1.41)/ 4 (load) = 64W - 22% (78% efficience) = 50W RMS

That power they call "music" power, that is the power if the supply can deliver continuous voltage, without any slow down...

And that's the difference between normal PSU (LARGE transformer with common retifier) and the SMPS Buck converter...




Waiting for opinions !
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Old 16th December 2005, 07:03 PM   #8
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Yes... Realy not easy, but I can build one supply for each channel, then it will be more easy...

I was looking PC supplys, that is of course, an offline buck converter, and the supply use 400v fast switching transistors, look:

http://www.ortodoxism.ro/datasheets/mospec/MJE13007.pdf

One ordinary PC supply can deliver about 200W, just with TWO of that transistors, ONE Mosfet (30v 0,022Ohms 40A) and a small transformer...

That's why I'm learning about switching buck converters, I think it's a real good solution, and the more important, it's REGULATED...

When we use the ordinary LARGE transformer, the voltage falls down very easily when we turn the bass and volume up, then the amplifier can't deliver the rated power...

For example, I made a stereo set for the computer of one friend, using two TDA2050, that each one deliver 30W @ 4Ohms @ 22.5v THD < 0,5%... Then I bought 18+18 4A transformer, after retification deliverier 27+27V... When the music was playing loud, the voltage falled down to 19+19... OK, but when stand by returned to 27+27 that BURNED the TDA after a while... Then I bought the 15+15 transformer that deliveried 22.5+22.5 in STAND BY mode, and when loud, 14+14v

Then, I rated the amplifier 19+19 W RMS.... Because:

Amplifier efficience is

22.5v + 22.5v = 45v
(45v / 2*1.41)/ 8 (load) = 32W RMS (100% efficience)

Ok, as the Datasheet says, the amplifier in these conditions above, can deliver 25W, so:

32 --- 100
25 --- X

X = 78,125 % of efficience.

Then

14+14v = 28v
(28v / 2*1.41)/ R (load) - 22% (78% eficience) = 18,5W RMS...

If I used the swithing buck converter:

22.5 + 22.5 = 45v
(45v / 2*1.41)/ 4 (load) = 64W - 22% (78% efficience) = 50W RMS

That power they call "music" power, that is the power if the supply can deliver continuous voltage, without any slow down...

And that's the difference between normal PSU (LARGE transformer with common retifier) and the SMPS Buck converter...




Waiting for opinions !
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Old 16th December 2005, 07:14 PM   #9
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Yes... Realy not easy, but I can build one supply for each channel, then it will be more easy...

I was looking PC supplys, that is of course, an offline buck converter, and the supply use 400v fast switching transistors, look:

http://www.ortodoxism.ro/datasheets/mospec/MJE13007.pdf

One ordinary PC supply can deliver about 200W, just with TWO of that transistors, ONE Mosfet (30v 0,022Ohms 40A) and a small transformer...

That's why I'm learning about switching buck converters, I think it's a real good solution, and the more important, it's REGULATED...

When we use the ordinary LARGE transformer, the voltage falls down very easily when we turn the bass and volume up, then the amplifier can't deliver the rated power...

For example, I made a stereo set for the computer of one friend, using two TDA2050, that each one deliver 30W @ 4Ohms @ 22.5v THD < 0,5%... Then I bought 18+18 4A transformer, after retification deliverier 27+27V... When the music was playing loud, the voltage falled down to 19+19... OK, but when stand by returned to 27+27 that BURNED the TDA after a while... Then I bought the 15+15 transformer that deliveried 22.5+22.5 in STAND BY mode, and when loud, 14+14v

Then, I rated the amplifier 19+19 W RMS.... Because:

Amplifier efficience is

22.5v + 22.5v = 45v
(45v / 2*1.41)/ 8 (load) = 32W RMS (100% efficience)

Ok, as the Datasheet says, the amplifier in these conditions above, can deliver 25W, so:

32 --- 100
25 --- X

X = 78,125 % of efficience.

Then

14+14v = 28v
(28v / 2*1.41)/ R (load) - 22% (78% eficience) = 18,5W RMS...

If I used the swithing buck converter:

22.5 + 22.5 = 45v
(45v / 2*1.41)/ 4 (load) = 64W - 22% (78% efficience) = 50W RMS

That power they call "music" power, that is the power if the supply can deliver continuous voltage, without any slow down...

And that's the difference between normal PSU (LARGE transformer with common retifier) and the SMPS Buck converter...




Waiting for opinions !
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Old 16th December 2005, 07:55 PM   #10
poobah is offline poobah  United States
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OK, consider this

Use simple bridge rectifier and large caps connected directly to 120 volt line... makes 140 - 170 Volts depending on load. The ripple can be very high.

For isolation use a "FORWARD CONVERTER"... basically a buck converter with a tranformer. build 4 of the forward convertors, one for each channel.

This will bring the size down, so you can find/obtain ferrites for transformers and inductors. If you run at 50 - 100 Khz, the size will

A forward converter is in the AN19 application note.
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