Author Topic: why would anyone do it the other way around ?  (Read 7710 times)

0 Members and 1 Guest are viewing this topic.

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15391
  • Country: za
Re: why would anyone do it the other way around ?
« Reply #25 on: February 05, 2012, 12:01:16 pm »
Bought from the Fong kong store ( actually the store is called Wan Long Wholesalers.........) a 12 in one USB charger kit. Cost a whole $5, and has a nasty 12V USB converter and a mains version. As well a lead with 12 different points on it, from a tiny little barrel to a proprietary one for a certain computer company that uses a 30 pin connector for everything. Bought as I wanted a spare phone charger for the car, and it will do all the phones I have, after cutting off all the unused connectors.
 

Offline Jon Chandler

  • Frequent Contributor
  • **
  • Posts: 545
    • Throw Away PIC
Re: why would anyone do it the other way around ?
« Reply #26 on: February 05, 2012, 06:47:31 pm »
to be honest whenever I design anything, I put a bridge rectifier on the DC input so it automatically corrects the polarity at the cost of a volt, cause I'm sick of getting people emailing me to say "I blew it up with my powerpack" so yeah I would love a standard

This of course works, but in at least one case, led to a lot of frustration.  I had a device with a coaxial jack marked "12 VDC" but no polarity.  Not wanting to blow the thing up, I disassembled it to figure out what polarity it needed.  Many screws later, I can finally see the circuit board: JACK - BRIDGE RECTIFIER - REGULATOR, etc.  Geez, yes, using the rectifier should have made it foolproof, but not marking the polarity made it much more difficult!
 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3932
  • Country: 00
Re: why would anyone do it the other way around ?
« Reply #27 on: February 05, 2012, 08:01:04 pm »
A bridge rectifier lifts your device's ground. If you power multiple devices from the same power supply, and you happen to have other ground connections between the devices these ground connections short out one diode in the rectifier (non-destructive). This in turn raises the output of the rectifier in the device by one diode drop.

Depending on how much current the device uses and what signals you have this can be rather undesirable.
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

Offline PStevenson

  • Regular Contributor
  • *
  • Posts: 229
  • Country: gb
Re: why would anyone do it the other way around ?
« Reply #28 on: February 05, 2012, 11:43:01 pm »
A bridge rectifier lifts your device's ground. If you power multiple devices from the same power supply, and you happen to have other ground connections between the devices these ground connections short out one diode in the rectifier (non-destructive). This in turn raises the output of the rectifier in the device by one diode drop.

Depending on how much current the device uses and what signals you have this can be rather undesirable.

nothing too sensitive, usually just 9 volt guitar effects and stuff like that, with those a lot of users prefer the ground to be lifted so using the bridge has another function.
it's good to know that though cheers.

@Jon I had a similar experience so I always mark things I use them in "use any polarity at x volts" one of my friends just recklessly plugs anything into anything and it's always okay but on the odd occasion I have done it, catastrophic failure!
I learned more from the EEVBlog than I did in school
http://youtu.be/s-TK0zaakNk
 Amp Hour Theme Song Full Version http://youtu.be/buKg2eAX4Z0
 

Offline electrode

  • Regular Contributor
  • *
  • Posts: 141
  • Country: au
Re: why would anyone do it the other way around ?
« Reply #29 on: February 05, 2012, 11:47:57 pm »
[...]one of my friends just recklessly plugs anything into anything and it's always okay but on the odd occasion I have done it, catastrophic failure!

Is this with unregulated plugpacks?
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf