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Class D Switching Power Amplifiers and Power D/A conversion

Need Suggestions for Class D Inductors
Need Suggestions for Class D Inductors
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Old 15th December 2006, 04:33 AM   #1
Tubist is offline Tubist  Singapore
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Default Need Suggestions for Class D Inductors

Hi Guys.

I have an opportunity to run a board using AD1994 Analog Class D from ADI.

Basically I am doing another (not audio) 2 layer digital board and using the excess PCB to run the AD1994 design. My main board is reflow process and I am running the AD1994 board concurrently "for testing purposes" to account to my company for the usage.

Most of the components selection is very straight forward.

However, I need suggestions for off the shelf inductors (shielded) suitable for this application. I will also appreciate suggestions on what specs to look for in a suitable class D amp inductors.

I am designing the AD1994 in mono-mode, which can go 80W into 2 Ohms.

Any suggestions and ideas will be welcome.

Thanks in advance!!
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Old 15th December 2006, 07:07 PM   #2
rogs is offline rogs  United Kingdom
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I've used these before -
http://www.farnell.com/datasheets/62120.pdf - seem to be OK for low/ medium power class D applications.
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Old 15th December 2006, 08:13 PM   #3
Gorilla is offline Gorilla  United Kingdom
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I have used Coilcraft (http://www.coilcraft.com/) to get samples before. They seem pretty good.

In terms of inductor selection, I wouldn't use ferrite based coils, especially in a non-post-filter feedback design. The more non-linear your B-H curve, the more THD.
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Old 15th December 2006, 09:17 PM   #4
LineSource is offline LineSource  United States
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What is the formula to calculate the size of the inductor you need, say for a 1 ohm load instead of 8 ohm, at x-watts, at y-clock_freq?
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Old 18th December 2006, 12:18 AM   #5
Tubist is offline Tubist  Singapore
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Quote:
Originally posted by Gorilla
I have used Coilcraft (http://www.coilcraft.com/) to get samples before. They seem pretty good.

In terms of inductor selection, I wouldn't use ferrite based coils, especially in a non-post-filter feedback design. The more non-linear your B-H curve, the more THD.
Hi.

Thanks for the suggestion, but I am primary concerned with the EMI from a air-core inductor, even for domestic use, as my setup, I do have a radio as my source.

In actual application, would the use of a air-core inductor be really bad and interfere with other equipment performance? If we are to put a metal shield around an air-core, would it help?

Thanks for any answers
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Old 18th December 2006, 01:34 AM   #6
zilog is offline zilog  Sweden
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Quote:
Originally posted by LineSource
What is the formula to calculate the size of the inductor you need, say for a 1 ohm load instead of 8 ohm, at x-watts, at y-clock_freq?

Read this link -> http://www.qsl.net/xq2fod/Electron/Magnet.html

I consider the output inductor a DC choke, you should use gapped ferrite or iron powder for linearity. Also design for a flux density of no more than say 0.2T at peak current to avoid distortion.
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