Interest in dual regulator LT1083 pcbs?

[h_a]

Hi folks,

I'm finishing a pcb-layout for a voltage regulated psu-board for dual rails (like +/-35V) which uses the LT1083/LT1084/LT1085 regulator (the high power (7 A) TO-3P variant) for both polarities. I'm going to power my power amp with it.

It is very small in size, currently 50x70mm, double sided, has very fat tracks (150mills for the regulated side), has well separated tracks (20mills average track clearance) and will be manufactured with heavy copper (70um).

One board gives both voltages (adjustable from +/-1.25V up).

This is the first time I'll order at this boardhouse, but I've heared the board edges are cut - not milled - so probably don't look that perfect as you're used to. However this does not have an impact on functionality (just looks).

Big advantage - they're cheap.

Cost depends on number of boards, rough guess is about 18 Euros per board for 4 pcs (that I need), of course dropping with every board that comes in addition.

I'm looking if there's interest, so we could order more boards and benefit from a lower price.

Have fun, Hannes

PS: I will post schematic and layout in the next few days.

[h_a]

Schematic

Please note that caps on the regulated side are necessary and that I did not provide space on the pcb for them. They should be mounted on the amp board anyway, so that they're close to the load.

[h_a]

Board

To be able to choose a suitable heatsink depending on the load, I think it's most comfortable to use an external heatsink, off-board to be flexible. So you can use something small for your preamp, but a real chunk of alu (1-2 K/W) for your power amp.

To be able to use thick or multiple cables I used the dual Molex-connectors in parallel for the outputs, so to get lowest resistance. For the ground connection I use a soldered connection.

Maybe some cosmetic changes are left to be done, but otherwise that's it.

I'm happy about every comment on improving it further!

Feel free to mail me directly if you're interested (or post here).

Have fun, Hannes

[jackh]

Count me in for 8 boards

[h_a]

Hi!

That's great, so we already have a nice number. I'll quote the board house today and see what they say.

All the best, Hannes

[h_a]

jackh, I just got the quote from the board house and sent you an email!

For all others that might be interested: with 12 boards we already cut the initial price in half, so at the moment it's 9 Euro per board.

All the best, Hannes

[agent.5]

I am interested. Have you considered:

[1] adding a protective diode between Vin and Vout?
[2] Maybe another diode parallel R1, and R2?
[3] Maybe space for a small cap (say 1000uf) after Vout?

[h_a]

Hi agent.5,

yes I've considered all your points; the diodes are not necessary for this regulator as it has an internal diode (capable of handling microsurge currents of 50A to 100A!). You can check this in the datasheet

2 reasons I didn't add a Vout cap: first this cap should be close to the load, preferable without parasitic wire resistance in between. 2nd there's simply no space! The size is fixed and you can see there's simply no space left! I would also have added the option for using the dual as 2 single rails, but same story.

If you're still interested, just let me know!

Have fun, Hannes

[peranders]

Originally posted by h_a
2 reasons I didn't add a Vout cap: first this cap should be close to the load,....

No quite If you read the datasheet you'll need a minimum required capactiance _close_ to the regulator. I can read 10 uF tanalum but in your case I would choose 10-100 nF/63 V polyester/ceramic plus 10-22 uF 63 V electrolytic cap.

[h_a]

Hi P-A!

Of course! That's the reason I use 2x 15A molex connectors in parallel for the outputs, to get the parasitic resistance to a minimum. Mentally I just add the cabling to the ESR of the cap, which is higher than some centimeters of wire anyway.

From reading the datasheet it is for me unclear why you want to use a bypass, since a 22uF Tantalum or 150uF elco gives perfect stability (as the datasheet says under all conditions). AFAIK Elcos have a rather weak high frequency response, so depending on the regulator this could be needed.

Maybe you could give me a hint on this?

Thank you very much, Hannes