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Old 10th July 2005, 11:43 AM   #1
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Default 1KW SMPS help needed

greeting to everyone

I want to build a 1KW SMPS power supply. The plan is to use a PFC preregulator followed by some form of isolation type regulator. I could use some help.

Fortunately, I've found 2 PFC reference designs from On semi that are each 1KW. The first uses the NCP1650 average mode pfc controller (and there is an available eval board), while the second used the MC33262 in critical conduction mode (no eval board available). It looks like either of these would work for me, but am interested in your opinions.

OK, so what about converting the PFC output down? I'm considering a few options:
1) A single supply for the entire 1KW
2) Multiple supplies in parallel
3) Multiple supplies, where each powers a different amplifier or group of amplifiers

Maybe some design details are needed here - the design is for a digital amplifier, probably 5.1 style. I believe the amps will use around 30-35 volts each. There is also some low voltage needs (microprocessor, for example).

Getting back to the supply configurations, I like option 1. My reseach indicates that a half bridge push pull setup would be a good choice. I'm having a tough time findind a good reference for this, however. Also, I am a little concerned about the danger at that power level.

Option 2 concerns me because I am not certain how to put power supplies in parallel without getting into load share problems. I see from other posts that there may be a synchronization problem as well.

Option 3 is neat, in that it is modular and expandable.

Any help or comments?

thanks

gene
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Old 10th July 2005, 04:51 PM   #2
mzzj is offline mzzj  Finland
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Default Re: 1KW SMPS help needed

Quote:
Originally posted by gearheadgene
greeting to everyone

I want to build a 1KW SMPS power supply. The plan is to use a PFC preregulator followed by some form of isolation type regulator. I could use some help.

Fortunately, I've found 2 PFC reference designs from On semi that are each 1KW. The first uses the NCP1650 average mode pfc controller (and there is an available eval board), while the second used the MC33262 in critical conduction mode (no eval board available). It looks like either of these would work for me, but am interested in your opinions.

OK, so what about converting the PFC output down? I'm considering a few options:
1) A single supply for the entire 1KW
2) Multiple supplies in parallel
3) Multiple supplies, where each powers a different amplifier or group of amplifiers

Maybe some design details are needed here - the design is for a digital amplifier, probably 5.1 style. I believe the amps will use around 30-35 volts each. There is also some low voltage needs (microprocessor, for example).

Getting back to the supply configurations, I like option 1. My reseach indicates that a half bridge push pull setup would be a good choice. I'm having a tough time findind a good reference for this, however. Also, I am a little concerned about the danger at that power level.

Option 2 concerns me because I am not certain how to put power supplies in parallel without getting into load share problems. I see from other posts that there may be a synchronization problem as well.

Option 3 is neat, in that it is modular and expandable.

Any help or comments?

thanks

gene
how about 2-transistor forward converter? less prone to explode if you have some problem with gate drive. downside is that max dytu cycle is 50% and average currents in coils, trafo, caps and switches are 2 times higher than in half-bridge or full-bridge. 1kW is well within reach with this topology.
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Old 11th July 2005, 06:53 AM   #3
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Without being a smps maven (yet, anyway), I am having trouble telling which topologies are best. On the 2 transistor forward design, I see conflicting info on power. One place I saw claimed it is good up to around 1KW, yet others said it is good up to a few hundred watts.

Can you help out on this front?

gene
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Old 11th July 2005, 01:48 PM   #4
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Default Flyback....

Hi gearheadgene!
I'm trying to do the same thing....
The topology I'm trying to use is Flyback.
I know this is not the best topology for KW designs, but I need to regulate several supplies, and flyback is OK for this purpose.

During my search I found a very useful page:

http://schmidt-walter.fbe.fh-darmsta..._e/smps_e.html

I hope it could help you.
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Old 11th July 2005, 04:18 PM   #5
Eva is offline Eva  Spain
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Have you done some calculations about the magnitude of the currents involved in a 1KW flyback and the energy storage requirements for the coupled inductor? The numbers will quickly discourage you.

Use a half bridge or full bridge topology with a coupled buck inductor instead, almost all multi-output computer PSUs above 150W are done that way.
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Old 11th July 2005, 09:27 PM   #6
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macc : I contacted a transformer manufacturer about building a flyback 1KW transformer. They pretty much confirmed Eva's reply. It would be big and expensive!

Eva: what do you think about the 2-transistor forward design proposed by mzzj? I think that the half-bridge approach is going to win, though.

Has anyone seen anything about Infineon's coolmos? Here's a quote from powerZone:
"Infineon is demonstrating a 1000 W (watt) reference design for a server power supply, with one 99 mΩ CoolMOS CS power transistor. . ."

Looks like this is brand new. So far, I haven't unearthed the reference design. I wonder what topology they are using. Can't wait to see it
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Old 11th July 2005, 09:50 PM   #7
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Quote:
Originally posted by gearheadgene


Has anyone seen anything about Infineon's coolmos? Here's a quote from powerZone:
"Infineon is demonstrating a 1000 W (watt) reference design for a server power supply, with one 99 m CoolMOS CS power transistor. . ."

Looks like this is brand new. :

No... it's not new. So called hi spec devices may sound fine until the gate impedance is worked out..i.e device requires higher drive v.s freq.
I've used coolmos in many apps with no real performance advantages other than lower Rds on resistance. The higher drain volts is a plus compared to standard 840 types.
The gate threshold voltage can be lower than standard types.

It all depends on the application.

richj
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Old 12th July 2005, 12:49 AM   #8
Eva is offline Eva  Spain
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I think that this single transistor 1KW PSU is probably a forward converter.
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Old 12th July 2005, 07:02 AM   #9
mzzj is offline mzzj  Finland
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Quote:
Originally posted by richwalters



No... it's not new. So called hi spec devices may sound fine until the gate impedance is worked out..i.e device requires higher drive v.s freq.
I've used coolmos in many apps with no real performance advantages other than lower Rds on resistance. The higher drain volts is a plus compared to standard 840 types.
The gate threshold voltage can be lower than standard types.

It all depends on the application.

richj

CoolMos is pretty damn fast, gate charge for same Rds-on is lot less because same Rdson is archieved with 5? times smaller chip.
Also output capacitance is substantially smaller.

This can be advantage if you want to run it real fast, or it can be problem if you have specsed your gate drive for similar conventional type mosfet and with coolmos it slews and rings like crazy. (resize you gate resistor in this case)


Btw, Fairchild has some damn pretty IGBT's availlable for SMPS use, especially their new SMPS-II series looks impressive:
FGH60N6S2
Features

100kHz Operation at 390V, 52A
200kHZ Operation at 390V, 31A
600V Switching SOA Capability
Typical Fall Time. . . . . . 77ns at TJ = 125C
Low Gate Charge. . . . . . 140nC at VGE = 15V

12kW SMPS anyone?
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Old 12th July 2005, 08:16 PM   #10
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Quote:
Originally posted by mzzj



12kW SMPS anyone?

Yes.....Viva IGBT's....= tram drive.

p.s .....Mosfet chip area is pretty inefficient compared to IGBT's for same current rating. I'm using IGBT's as standard in my switch mode /pfc designs. In well disgned layouts one can scrap the series gate resistor with IGBTS. However I can recommend a mosfet/IGBT driver interface.
The secret is all in the layout.

richj
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