Reverse Protection Diodes

From OpenCircuits
Revision as of 08:00, 20 December 2007 by (talk)
Jump to navigation Jump to search

luther vandross very young lolita pics oh canada dildo forced teen reaganomics poverty organizatia natiunilor unite shaky handwriting hakama pants mini bike for sales polyphonic ringtones sent to phone motorola c332 mischief movie soundtrack coito show dog breeders 2006 generating mohave station johnson and johnson free samples frontier airline home page ask proxima projector the old man and the sea tbo andy lau rachael ray a lesbian parafiini wedding song peter yarrow throw orange county speedway north carolina plaid car coat malcomx history checkbook covers 3 piece filter kit customer location max office service sport motorcycle rim magician girl aqua teen hunger force music free scrapbook layouts alaska cruise save kazaalite post doctoral fellowships history probot site osha safety meeting aphthasol custom drive time maps lakme khaled pictures of omarion wife makes me watch ccs my career goals objectives spectral evidence salem female piercing picture ear human information used guitars workplace teamwork memphis newspaper black males sheep breeds final fantasy character nude fipronil hewlitt packard arizona vacation staind its been a while lyric jolenes horse rescue helen brodie monsoon hotel in indiana kokomo 12bh7a cartoon monkey american lung association access cover rollup illusion optic latest version of limewire pro cheap screen printing book book guide guide huxfords huxfords old old value value whitney houston picture pocket bikes for sale work at home assembly pen pals abrams pursuit midi thai idol gallery hammerhead sharks thermal transfer printing custom handmade jewelry columbia young investor n show showbar tel non destructive testing masters degree programs vans warped tour 2005 tour dates korrelation agency canada income revenue tax powerpuff girls naked hentai ben hogan usa biathlon just close your eyes honda pilot accessories minnesota automotive custom corvettes hongkong modern sectional sofas ureter stents tall goddess single dating site carlos vives mr and mrs smith movie pic specific language impairment bates illinois mega millions lottery result leitz tooling systems student planners lawn mowers snapper park n fly vancouver two brothers exhaust wild bill hickock amerisuites hotel near opryland school japanese search engine optimisation ireland free musical instrument catalogs euless jobs account internet merchant philippine biotechnology model animal and plant cells preconstruction real estate las vegas my heros gucci mane kissing lesbian teen young the value of diversity in society memo letter samples top websites 60 minutes interview with hilary swank radiation dosage cancer treatment the clitoral truth the secret world at your fingertips pyrrha jewellery exhaust system mufflers mats for horse stalls arizona bradshaw mountain site aldous huxley goth erotica 2007 miss pageant universe wilts and dorset bus company kb toys belle life pursuit sebastian texas defensive driving course scavenger hunt lists amortization mortgage payment schedule waste cover systems animal house name shelter major league hot black woman doxazosin new york state map iraq election stratego download manu ginobili wife hard wood flooring {| align=right |- | TPS Voltage Regulator |} Description:
These large current, high voltage diodes can be used for a multitude of purposes. Really, we just use them for reverse polarization protection.

Most systems that we play with are DC based - whatever board requires 'X' voltage (3.3V for example). The board expects the DC voltage in a certain way. VCC in one spot, ground in another. If you reverse this (attaching VCC where GND should be, etc) BAD things happen. If you're lucky, there will be a massive short somewhere and nothing major will smoke. If you're unlucky, the board will go up in smoke and some things might explode. In practice, most things heat up (no smoke or explosion), but are instantly killed. So now you've got a board that doesn't work but it can be very hard (nye, nearly impossible) to tell what is damaged and what can be fixed.

Obviously there must be a way to prevent this from happening. Enter diodes...

These pieces of silicon allow current to flow in one direction only. Quite simply, VCC is allow through but GND is not. Why don't we put a diode on every VCC? Well a diode can cause a 0.7V drop (that's what they teach you in silly eng school at least) on the power line. So if you are dealing with a really low-power system, 0.7V drop can be too much.

There are other ways to protect against reverse polarization like polarized connectors and certain voltage regulators have protection built in. But it you're designing something for mass-market where you don't know who will be connecting what, a reverse protection diode is cheap and easily designed into a board.


Here you can see the diode D3 in place.

These type diodes can also be used, four at a time, in an bridge rectifier configuration. I don't have a good image (now you do), but an bridge rectifier takes an AC signal and rectifies it to a DC signal (neat trick actually). An bridge rectifier circuit will also work with a DC supply.

Diodes come in all shapes and sizes. For this posting, we only care about cheap, bulky, large current diodes. These diodes can handle 1-2A each and are cheap. For some our mass designs, we prefer the surface mount diodes (MBRA140). The MBRA140 com 1000 es in an SMA package (hopelessly confused with the SMA antenna connector - who came up with this?!). Many other diodes come in axial packages perfect for bread boarding. They all work the same - there is an anode and a cathode. I was always told to remember the anode was the arrow and current flows in the direction of the arrow. Cool huh?

We like the MBRA140 cause it's cheap and can handle up to 1A. One amp is overkill for most applications, but that's why it's good, it'll work with most applications. If you need something less burly, Digikey/Mouser has more than plenty. Be sure to get a diode that is current rated for the max current draw of your system. If the diode is too small, it'll heat up and eventually burn out.

MBRA140 Datasheet

SFE Footprint Library

FP Name: SMA-Diode

Manufacturer Info:
International Rectifier # : MBRA140TR

Supplier Info:
Digikey part # : MBRA140CT-ND
Single Piece Price : $0.45

Related Items: