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Old 5th February 2013, 06:22 AM   #1
Astera is offline Astera  United States
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Default Linear Power Supply - How-To

Can anyone point me to a resource where I can learn about designing and building a linear power supply for Class-D amps?

I've seen lots of photos of amps with toroidal transformers and banks and banks of electrolytic caps. I understand you need both + and - rails....

I know little else. Where did you guys learn to make your power supplies?
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Old 5th February 2013, 06:50 AM   #2
Mooly is online now Mooly  United Kingdom
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Firstly you need to define your requirements.

Voltage output required. (And not all amps need a - and + supply, particularly Class D).

Current required. That will depend on the max power output of the amp mainly, and that would be used as a basis of calculation.

Lots of caps. Not necessarily.
A lot of that thinking is "fashionable" but can bring its own problems. What you really need to know is how much ripple is acceptable and use that to help decide. If the supply need to be super stable and/or totally ripple free then a regulator of some sort is required is required.
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Old 5th February 2013, 07:09 AM   #3
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Whether or not a bipolar + & - supply is needed depends on the circuit to be powered. Just like there are single-supply op amp circuits and dual-supply op amp circuits.
If you don't have any books handy (virtually all semiconductor device and general electronics texts will have some ps coverage), look for online tutorials and manufacturers' web sites. Makers of transformers, diodes, and linear regulators will usually have application notes that teach design procedures. Here's but a small sampling:
Power Supply Design Basics
Understanding Linear Power Supply Operation
ESP's Linear Power Supply Design
UNLV's Linear Power Supply Design
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Old 5th February 2013, 05:48 PM   #4
Astera is offline Astera  United States
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Thanks. I have an older (Radio Shack) book on power supplies. I know the general drill for a linear PS: transformer, rectifier (full or half-wave rectified) some filter caps + resistors to reduce ripple.

The power supplies I've seen posted in here (in the Class D Amp Photo Gallery for example) show a lot more caps then I am used to seeing ... on a tube amp power supply for example that may only have three large capacitors.

I should have said I intend this for driving a Sure amplifier board. Now that I look closely though, they don't require a bipolar PS....

Does anyone have a schematic they can point to that uses lots of fashionable caps?
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Old 5th February 2013, 08:13 PM   #5
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You don't really need a different schematic, I don't believe. The basic thought behind the cap grouping is that rather than sourcing a single large cap, say 100000uF, instead ten 10000uF or twenty 4700uF are used. The parallel grouping adds the capacitance while reducing the total ESR and ESL. The layout becomes more important than the schematic in optimizing the function.
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Old 5th February 2013, 08:23 PM   #6
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Quote:
Originally Posted by Astera View Post
Does anyone have a schematic they can point to that uses lots of fashionable caps?
LM338 based are simple

http://4.bp.blogspot.com/-lyT-ij3grU...sing+LM338.jpg

You don't have to use one 10 000 uF cap.
You can use 10 x 1000 uF or more.
lm338 needs heatsink.
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Old 5th February 2013, 09:04 PM   #7
Astera is offline Astera  United States
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Thanks. And I learned about ESL and ESR today as well. I'm guessing the power supplies I've seen where there are a lot of smaller electrolytics were for switching power supplies as I don't see the impact ESL and ESR might have on a linear power supply.

The LM338 looks to be the more or less standard PS I'm used to.
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