SparkFun Forums

[geekything]

Are the BoMs really the same, except for the regulator itself?

-marc

[geekything]

I should probably clarify...

Ordered one 3.3vdc and one 5.0vdc breadboard power supply. I know from the product description that the boards will both have 5vdc on the silkscreen -- no problem. But the resistors/capacitors for both boards are also the same -- although the regulator is different (one 7805 on LM317T).

Is this just a clever design where the LM317T's variable output is pegged at 3.3vdc based on the resitor/capacitor network and they just happen to be adequate for the 7805's needs too?


-marc

[Pete-O]

I didn't design that board, but we don't normally use LM317's for regulating. Where did you see that? I can't find that part number in the description.

Pete

[upand_at_them]

I like those breadboard power supplies; they're pretty cool. I have a similar one that came with an electronics book.

Any chance on making one that's switchable between 5V and 3V? Or throwing a pot on there to make it adjustable?

Mike

[geekything]

I didn't design that board, but we don't normally use LM317's for regulating. Where did you see that? I can't find that part number in the description.

Pete

The part number isn't on the description. It's on the regulator. I have what are supposedly one 3.3vdc and one 5.0vdc unit that I recently ordered and am trying to establish I've been misshipped two 5.0vdc units before I build.

The LM317T *is* variable output, and can actually do both output voltages.

-marc

[pittuck]

Hummm, ok well is your bare pcb the same as the one online?

If so there are no resistors to make the referance voltage so i would not have expected the 317 to be used!

Further more with the low end power supply (6V) and the series diode (0.7V drop) u get 5.3V the lm317 i think needs about 1.2V above output to work efficiently.

So using the lm317 *should* only be with 3.3V applications! I would expect a low drop out variant of the 7805 for the 5V type as its much cheaper.

[pittuck]

Just had a look on the sparkfun shopping store and have found they have the LM7805 and LM7833, 5V and 3V regulators.

With my earlier comment, the LM7805 should have a 2V drop out, so supply should be >7V....

The 3.3V one is 2V too making a minimum input voltage of 5.3V

[geekything]

As a follow-up: I followed the traces on the board and nothing is connected to the centre pin -- therefore no reference voltage. So this definitely is a fulfillment problem.

-marc

[pittuck]

Ok, so there is the possibilty sparkfun sent a LM317 instead of the LM7833 or LM7805

[geekything]

Or whoever does their fulfillment. It's also quite easy to mistake one regulator for another

The PCB is the bit that's important to me -- I can replace the regulator with one bought at my local electronics store.

But if someone from Sparkfun can investigate, it might stop others getitng a regulator that will only generate 1.25vdc

-marc

[sparky]

Hey Guys!


Please email Jeff at fun @ sparkfun.com and call him many icky names. He stuffed the kits with the wrong regulator. We'd be happy to send you a free LM7833 regulator.

The 5V kits are correct.
The 3.3V kits were shipped with the wrong regulator up until I noticed them on the 15th or 16th (last week).

Really really sorry,
-Nathan

PS - Where do we find customers like you guys?! Any other customers at any other company would be calling and yelling at us. You guys sit down and have a discussion about PCB traces and the inner-karma of a variable LM317 regulator! Thanks so much!

[geekything]

Heh...the reason we like Sparkfun is the curious minds we have

As a follow-up: Sparkfun added a free LM7833 to my recent order to rectify the problem and apologized for the error in an email and got a free LM317T to boot. Satisfactory end to a bit of a saga.

Oh, and Nathan confirmed that indeed the BoM for both the 5.0vdc and 3.3vdc breadboard power supply kits is indeed the same apart from the regulator itself.

-marc