[Voodoochile]

Hey, I said this was going to be minor... I finished up the NAPS-1 using the board I made with trimpot pads for setting the output. While I was poring over the datasheets for the Linear Tech regs, I noted that there was mention of how critical it is to keep the 'feedback' resistors (R1 and R2 in this schematic) as close to the output pin as possible. Solder it directly if possible, to maintain the best regulation performance, in essence. Well, by swinging D1/R1 and D4/R2 90 degrees, the schematic is basically unchanged, but the resistor it at the pin, instead of 3/4" away, and after the junction of the diode.

I'll probably move this (layout) around a bit to allow the parts to lie down before I use this again, but it was quite straightforward, and it does check out to be tighter regulation, though I am starting to split hairs here. A detailed picture is here, and for reference, the original parts positioning is shown on this version, which is stock, no trimpots.

Just a thought for anyone building a similar PS, even if they were to build the actual PS1, this mini-tweak would work on the commercial board as well.

edited for crummy typing

 

[jamont]

Nice picture!

How much difference do you measure in the regulation after this mod?

 

[Voodoochile]

On the regular one (second link) the drift is about 0.1 volts max. After turning the Rs and diodes, it is down to about 0.04 (15.03 to 15.07).
I don't really care for tombstoning, but it would be easy to spread it (board layout) out a tad to fit... maybe even just drill another hole further up the trace to accommodate the outer leg.

 

[Ghostie]

"tombstoning"
Does that mean standing the resistors up?

Ghostie

 

[Voodoochile]

Yes, that's it.
R.I.P.

 

[Voodoochile]

Got a couple requests for part numbers... here they are:

The ten .01uF bypass caps are BC2132-ND
The two .33uF MKPs are BC2079-ND
The two .47uF MKPs are BC2083-ND
The eight hexfreds are HFA08TB60-ND
Terminal blocks are ED1627-ND
Two 20k trimpots are CT9W203-ND
Heatsinks are HS220-ND
Positive reg is LT1085CT-ND
Negative reg is LT1033CT-ND
Dual 15v tranny is TE62073-ND (2.332A) ...or...
Dual 18v tranny TE62084-ND (2.77A)
Diodes are 4007/whatever you have that is appropriate
Other four resistors are all 1K ohm 1/4 watt metal film 1%

The 15v toroid makes about 21.25 volts after rectification, the 18v makes about 25.5.

Please set the value on your trimpots to 10k (if you want about 15 volts out) before installing them- save you some headaches later on. Also, the pins are not staggered. Place pins 2 and 3 in the ground and pin 1 on the adjust leg in order to ensure that clowise rotation gives you More Power.