Parts Questions

[Siegfried Meier]

Hi Tim,

The following are backordered from Digikey for 4 months!

P10730-ND
LM317TFS-ND

I think I've found the regulator at a local electronics store, but the part only says on it:

PM34AX
LM317T P+

Is this the same part as I need?? They're also looking into the caps to see if they can get them. 4 months is ridiculous. I'm not waiting that long to fire this thing up. Thanks Tim.

Best regards,
Siegfried Meier

[tele_player]

There's a good reason to buy complete kits or assembled items from Seventh Circle whenever possible. Waiting for backorders, and/or hunting for parts is annoying, I'm about 5 small parts away from having two complete J99 modules. I expect that to go down to 1 or 2 parts in a couple of days, when my last tiny order comes from Digikey. I started on these over a month ago.

[tpryan]

You can substitute a P11005 for P10730. It's slightly smaller in value, but should work OK.

If you type "LM317T" into Digi-Key's search engine, you'll find four possible parts. All will work, but the Fairchild is out of stock.

[Siegfried Meier]

Thanks Tim. If a complete kit had been available for the PS02, I would certainly have purchased it. However, I did want to build the PS myself so this was the only option. Thanks again.

Best regards,
Siegfried Meier

[Siegfried Meier]

One last question regarding the regulators and their mounting. Should I lay them in this order: heat sink, thermal pad, regulator, and then the flat black washer, with the screw over top of that? Is the idea so that the regulator never touches the heat sink, which in turn is mounted to the board? My apologies for this seemingly obvious question. Thanks.

Best regards,
Siegfried Meier

[tpryan]

Yes, that's the idea. When U1 and U2 are assembled to the heat sink, you should measure an open circuit between the regulator tabs, as well as between each regulator tab and the heat sink.

For U3, the LM317HVT, it's better to put the thermal pad down first, then the heat sink, then the regulator, insulating washer, and screw. That's because there is a PC trace that runs right along the bottom edge of the heatsink. If you're not careful, you may get the heatsink on top of the trace, which might possibly cause a short someday. Putting the thermal pad under the heatsink eliminates that possibility.