Help needed finding power inductors for PWM amp

[Amphiprion]

I know we have some SMPS guys on the forum. I'm having trouble finding/selecting inductors for a Class D amplifier. Switching frequency is 384kHz with about 95% modulation range, 100W 8ohm / 200W 4ohm desired; values are 10, 15, and 22uH shielded ferrite inductors needed for 4/6/8 ohm applications (BTL mode so 2 inductors per channel). Power supply voltage is up to 50V (well, 48V probably from a switcher).

Toko makes some nice ones for digital amps (DASM1620 series), but I can't obtain them. The DR127 style by Coiltronics I'm afraid will have too many losses and overheat, but that is one of the very few shielded ferrites that comes remotely close and I that I have no trouble obtaining.

The SER2900 series from Coilcraft looks great from a loss perspective, but it's absolutely huge (hence the low losses) and I'm not sure how good the shielding on them is. I don't want to be hosing up the FM band if I don't have to.

If anyone has any hook-ups through their day jobs for getting power inductors, especially from Toko, I would really appreciate any help. Thanks!

[Hank]

Hey Kid, I just sent a note to our electronic components commodity buyer to see if one of his distribs carries Toko.

[Hank]

I just sent you an e-mail with our electronics commodity buyer's Avnet contact information. I hope your project doesn't go up in smoke when you power it up! :lol:

[Amphiprion]

Thanks Hank! I have been getting the cold shoulder from some customer service rep at Avnet, essentially 'buy 1ku or go home' was the response. Hopefully your contact can get me the hook-up. Surely they deal with people wanting prototype/engineering samples often enough. Who buys inductors at 1ku quantities for $5ea just to find out their product fails in the EMI test chamber?

I'm learning way more about power inductors than I ever really wanted to. I might even roll my own if I can't lay my hand on some good commercial units. Of course then where do I obtain nice gapped ferrite toroids or other cores? Sigh....

[Hank]

You gotta remember that these big distributors live on volume business. If it's an engineer at a company wanting to buy a few items, it's ok, because it might result in volume. But these distribs get calls from individual hobbyists all day long and can't afford to deal with them.
If you roll your own, what torroid shape do you want? I've bought some torroids for AC filtering off eBay recently, so maybe there are other types available.

[Amphiprion]

I know - I'm doing a helluva job pretending I'm a big company!

I'm not sure what kind of core I want yet should I roll my own. I have the eval board for the TAS5518 and two TAS5261 power stages here, I just need to order some dummy loads from Parts Express so I can do testing at full power and see how hot various inductors get. I'll also be trying it with some of the commercial inductors I can get my hands on.

[Dennis H]

I just need to order some dummy loads from Parts Express so I can do testing at full power and see how hot various inductors get.

I don't know how much power you're talking about but I like ChasW's dummy load for testing big amps. He uses water heater elements in a bucket of water to keep them cool so the R doesn't change.

[Amphiprion]

That is a pretty inventive rig. Fortunately I don't need anything more than 200W. I'm just waiting for the dummy loads at Parts Express to get in stock next week. They're nice and small and the same thing I used to use at Cirrus for our power amp testing. The TAS5261 is a max 200W@4ohm chip, and I doubt I'll ever build anything more powerful.

Besides, all the buckets around here are reserved for fish tank work: