Reply to "Narrow Version of DIY 317 Voltage Regulator Board, with Build Files"

stan2004 posted:

I realize the train has left the station, but two other comments for the record.

1) Will a 3296W trimpot physically fit in the space allotted for the 3362P - without bumping into the cap or bridge?  It's a little longer/wider and it would require a new pad to be dropped on the board since the terminals are in-line albeit on a 2.54mm grid.  The idea is to allow either style of trimpot to be inserted.  The 3296W is multi-turn as used in the ubiquitous LM2596 stepdown regulator modules that we have come to know and love.  Same cost on eBay when I just looked. This might be a nice project for someone getting started with DipTrace and could take Rod's existing design and make a minor modification with a high likelihood of success while contributing to the cause (in my opinion of course).

2) For some applications with low-current, it might make sense to install the TO-92 version of the LM317.  Might be even cheaper depending on where you buy.  The idea here is very few designs come anywhere near requiring the >1 Amp capability of the LM317T.  In fact I seem to recall real-user data where the current required in a passenger car LED application was 5 mA (or less)!  In such a case there's no need for the TO-220 version which of course is a rather large package.  Commensurately, you would not need a 1000uF capacitor to achieve a suitable flicker reduction...and could use, say, 220uF or less which would allow even a smaller overall space requirement.  Again, the idea here is to create what amounts to an Application Note for Rod's board design.  I suppose if someone learning DipTrace wanted a simple modification project to get one's feet wet, they could add 3 pads on a closer grid to install either the TO-92 package or the TO-220 package (same PCB board)...and contribute to the cause (in my opinion of course).

Good suggestions Stan; my take for what it's worth:

1) I haven't tried to implant the 3296W trimpot, but may give it a whirl. IMO the readily available 3362P pots are nice and compact, and offer only a 270 deg turn from max to min, and will allow 0.1 volt output resolution in this circuit, so that's what I went with, for now! That's only me though.

2) This board was not really intended for low power apps like led lighting. Grj's constant current board already does a great job of that. This board was intended for GP vreg use up to about 500 ma, AC or DC input, engine, car, or trackside mount. Having said that I tried adding the TO-92 pattern, as well as grj's suggestion of a single diode pattern over the bridge diode pattern. Here is what I came up with:

Vreg Narrow R2.21 Snip

This is certainly workable, though I had to scrunch the components a bit to kept the new length down to 48mm, just under 2". But it fits and it would work. Width is still 1/2". I used a DO-35 pattern for D2 and angled it as you see to take up less space. 

But then I got thinking, is this really necessary? The TO-92-100 pattern has the same pad spacing as the TO-220, and the pinouts are the same. So why not just stick the TO-92 leads into the same holes and call it done? Sure, the TO-220 drill holes are bigger than needed for the small version, but no big deal. Then I tried doing this fit and a 1N4002 diode across the ~ and + pads of D1. Here is the mock up:

IMG_1592

As you can see, it's a no-brainer fit. This of course is not the same board as posted above, but you get the idea. For a low power 317L version, you could just use a 1N4148 diode for D2, which would be even easier to fit.

I see 4 power options available in using just the bridge diode pattern as it stands:

1) Full wave AC to DC, with isolated grounds, using the bridge diode.

2) Half wave AC to DC, with common ground, using a diode as pictured, and a wire jumper from ~ to -.

3) Straight DC input using jumper wires for both sides of the bridge pattern, as per 2).

4) Straight DC input with the bridge in place, accepting that there will be a 1.4 volt loss in feed voltage to the 317. 

This is pretty good versatility. All in all, I really don't see a burning need to put yet another set of Gerbers out there, but that's only my opinion of course!! If we think it should be done, by all means I will put them here for rtr12 to add to the sticky post of build projects. 

Rod

Attachments

Images (2)
OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
330-757-3020

www.ogaugerr.com
×
×
×
×
×