Truckputer? - Initial Schematic and PCB design - Post 28

[Fordum]

(with the resistors being the most thermally unstable most likely)

There is no doubt that the resistors would be thermally unstable, but in this configuration, as long as they were kept close to each other, wouldn't the regulation be good?

A very long time ago, I did a paper on resistance vs temp on carbon resistors, but I don't have a clue what I wrote.

But, I seem to remember that like wattage and types varied almost identically with temp.

Here is a circuit I found for that type regulator. Its for a different model, but it works the same.

If you notice, the output voltage is, I think, determined by the ratio of the two resistors.
So, if they both varied the same amount due to temp, the output would stay the same.

It almost has to work this way due to the claimed regulation. I don't see how it would be that tight if you were depending on a resistor.

 

[Jagged]

Ended up switching out the 7805 for a 1117V50 to match the 1117V33. For my instrument amp I'll just use the adjustable version 1117AV. I also went ahead and changed the resistors out for 1/4 watt resistors.

I'm pretty satisfied with how the board design is now. I added some requisite LEDs (what's a project without LEDs??!) for indicating 12V, 5V, and 3.3V power.

I don't think I could cram anything else on this board

 

[Fordum]

Sounds good. Of course you are still stuck with the nonstandard pinout, but at least its consistent with all the regulators.

I don't believe I have ever used any of those. I looked at one one time, but the low output current of either 800ma, or 950ma, depending on what data sheet you look at was too low.
Plus it had an absolute maximum input voltage of 15 volts.

With my alternator putting out 14.5, supposedly, it was just too close for comfort.

I considered either putting in a 12 volt regulator for my regulators, or a 15 volt 5 watt zener with a heavy resistor as a crowbar, but just said the heck with it and used a 7805 with extra capacitors for stability.

Tighter regulation was all I was looking for anyway in that particular case.

Do you have a particular company in mind to do your boards? I never had enough boards to build to make it worthwhile. I just used the iron-on resist paper.

Of course, back then, with no computer processing machinery, it cost a mint to get a board done even if you had the completed file to send them.

Probably a lot cheaper now.

 

[Jagged]

Ehh. It's still $45 for 3 boards if you're prototyping through the current major vendors.

I'll be etching my own until I get the design validated. Once I know it works, if there's any interest from others for parts kits, I can get someone else to make the boards. If it's just for my own good, I'll continue etching my own. I can use a spray-on conformal coating to protect the boards after assembly.

 

[cdoggwsu]

Ever get this working, Mitch?

 

[Jagged]

It's in my folder of neat things to build.

I'm up to my ears in schoolwork and research right now. Maybe this summer I'll have some time for it.