Hi Freaks,
Just discovered something while building my LM7805 supply. I have two wall wart (AC adaptors)
a) Stancor(12VDC, 200 mA) and b)CUI SMPS 12V 1.5A.
a) has +----(0----(-) on the barrel connector and
b) has (-)---(0-----+ on it.
I assumed both to be the same and plugged them in. Luckily, I had my protecting diode. I wish they had the same convention for all wall warts..Anyway thought I would share this with the community. :)
yep, there is not standard there. So you must always look at the supply to see if it is center positive or center negative.
Which makes me wonder, how have they connected the barrel connector on the STK500? The kit works no matter which wart I use.
Boards like the STK500 have a bridge rectifier after the connector so that AC or DC of either polarity can be used.
If you look at the board with the connector facing you. It is the square part to the left of the connector that has 4 pins. 2 marked with "S" like symbols indicating AC, and + and - markings on the opposite side for the DC outputs.
Ok that makes sense. Thanks for the explanation, Glitch.
The different polarities of the coaxial power connectors is the easy part. All devices I have that use them show the polarity, along with the voltage, etc.
But these connectors come in two sizes that look identical. The outer contact is always 5.5 mm in diameter. The inner contact can be 2.1 mm or 2.5 mm in diameter. I can't see the difference with my eyes.
To find out what I have, I test them. A 2.1 mm plug won't fit into a 2.5 mm jack.
A 2.5 mm plug will fit into a 2.1 jack, but I don't know if it makes good contact.
Now that I think about it, these connectors are hermaphroditic. Each has a male and female part. Maybe that's why they always seem peculiar to me. :)
A 2.5 mm plug will fit into a 2.1 jack, but I don't know if it makes good contact.
So, no, it doesn't make good contact (at least, not for me).
Don
That's a good point.This is a different post, but why don't they standardize this?
Also I like the fact that the connector has three pins which makes it easy to fix to a breadboard.
If they made standard wall warts then you wouldn't need a specific one for each product. ($$) :wink:
Seriously, the proliferation of designs is awfully annoying. There are barrel sizes, internal sizes, length, ac/dc, voltage, current rating, and polarity. Not to mention that there are still some with male connectors.
Don't expect standardization anytime soon. A consortium of cell phone manufacturers ( not imcluding Apple) is working on standardizing charging connections for cell phones -- should start to appear in 2011!
Don't expect standardization anytime soon. A consortium of cell phone manufacturers ( not imcluding Apple) is working on standardizing charging connections for cell phones -- should start to appear in 2011!
I suspected as much. I find a lot of these plugs and jacks are out of spec to start with, and give bad results no matter what you do.
From my experience I guess the 2.1 mm connectors are more popular than the 2.5 mm, although I have some devices that use 2.5.
As far as tip polarity goes, I think tip positive is much more popular. I don't think I currently have any devices around here with tip negative.
IIRC The standard for adopted for cellphones is the micro-usb connector. It was an easy choice, as most (smart) phones already sport a USB connector of some form or other.
IIRC The standard for adopted for cellphones is the micro-usb connector.
I recall reading that China mandated micro-usb connectors for all cell phones, starting a few years back. And they also banned plastic shopping bags. Remind me why we're so convinced we're more civilized in the West?
It would be very nice to see the EU or the US force manufacturers to adhere to certain standards. Things like Dell's needle adapter don't seem to make any sense whatsoever, aside from vendor lock-in.
