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Old 18th October 2014, 08:06 PM   #1
mohits is offline mohits  United States
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Default First 24V Power Supply

Hello everyone,

I am starting building a 40W 8Ohm chipamp for bookshelf speakers. It will need a 24V power supply (12V/-12V for two-rail operation). So, to build a power supply, I need to get a transformer. I looked up on mouser and found thiese results:
Transformers | Mouser
Digikey results:
Power Transformers | Transformers | DigiKey

Since I hae not built a power supply before, do you think I am looking at the right transformers? Also, what considerations do I need to choose which transformer to buy? Do all transformers upply positive and negative rails?

Thanks!
Mohit
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Old 18th October 2014, 08:25 PM   #2
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The Mouser transformers appear to be single-secondary types. For a bipolar supply, you'll want a center-tapped (or dual) secondary. The DigiKey page shows those (dual secondary types).

Do you have a psu schematic you will be using?
The load and the psu circuit itself (for example, ripple filter components, regulated/unregulated output) are the most basic factors involved in transformer selection.

Transformers supply converted and/or isolated AC voltage. The circuitry afterward determines the kind of DC output.
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Old 19th October 2014, 04:42 AM   #3
mohits is offline mohits  United States
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Thanks for your tips. I am using the circuit based on this project:
DIY LM3886 Chip Amplifier (Gainclone) Kit
The power supply is in Figure 2.
For the amplifier, I plan to use LM3875, and use the circuit from its datasheet. http://www.ti.com/general/docs/lit/g...5&fileType=pdf

Hope the amplifier and psu are compatible
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Old 19th October 2014, 05:24 AM   #4
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The power output depends on the powersuply voltage and the speaker resistance. If you
use your proposed + & - 12v supply you will get nothing like 40w. Looking at the data sheet even if you use + & - 28v you only get between 30 and 38w . So your 12v + &- will only give you something in the 5 to 10w range. I would be looking for something like 48v ct transformer at at least 150va. You might look at 2 of the toriods on this page one with dual 24v outputs and another with dual 28.4 outputs ( you can wire the secondaries in seriese for a center tap transformer) miscellaneous.html
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Old 19th October 2014, 06:01 AM   #5
mohits is offline mohits  United States
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Thanks for the correction. Yes, I based my values based on calculations in page 21. It recommends power supply of +/- 30V. I mistook it to just 30V-gnd (+15/-15V).

Looks like I have to redo my transformer search.
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Old 19th October 2014, 06:14 AM   #6
mohits is offline mohits  United States
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After a quick search, I didn't find anything on Mouser, but only this one at digikey:
VPT48-1040 Triad Magnetics | 237-1335-ND | DigiKey

Does this sound about right to you?
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Old 20th October 2014, 12:17 PM   #7
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Did you click on the miscellaneous.html at the end of my previous post? It takes you
to our good friend Apex jr. who has bargens on transformers and capacitors.
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Old 20th October 2014, 07:02 PM   #8
mohits is offline mohits  United States
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I completely missed that earlier. It is very useful. Thanks also for pointing out the relevant transformers in his list.
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