high efficiency/low loss diodes

I know (think....) this has been covered in some from previously on the forum, I searched the archives but can't find anything. I need to use a diode for reverse polarity protection but I can't afford much voltage drop through the diode. Is there such a thing as a high efficiency/very low loss diode?

Schottky any good?
They come in various shapes and sizes from signal to power.
Please deifne "much voltage drop". Is there any other way round this?

bat 85 is really cheap (200ma) about 0.6v drop from memory

cheers

miles
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glass pipe

best thing is to check out DATA SHEETS so you can find something to suit your current (haha) requirements..

Low drop diode

A regular silicone diode drops 0.7V but a Schottky diode, like the BAT 85, only drops about 0.3 V.

Cheers MFB, I knew someone would know for sure, I should have checked or really known as it's as obvious as the nose on my face when a standard silcon one is around 0.7v, hehehehe

Miles
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vaporizer

This is why I always say read the DATA SHEET to get the gen. Obv it depends on manuf, but here goes for Phillips/nxp BAT 85:

If ------ Vf
0.1 mA -- 240 mV
1 mA -- 320 mV
10 mA -- 400 mV
30 mA -- 500 mV
100 mA -- 800 mV

So, as you can see, it depends on the load (and temp).
And Cisco's guess was nearer the facts
Different manufs will vary.

Brendan hasn't mentioned current, so he may need a different type, and that will have a different spec.
NEVER read a component 'headline' spec in isolation. It's merely your starting-off point.

Same goes for std silicon diode or anything, even the nose on your face

dippy many thanks for the definative answer, I'll be ripping the BAT's off some of my small solar panels, at 0.8 out of 6v is a fair percentage, I'll have to have a dig into the parts box to find something better at 200ma

cheers

miles
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BMW E70 picture

bought some of these the other day for 20 pence for 5, knew I'd find a use

between 0.2 and 0.4v drop


http://cgi.ebay.co.uk/30WQ03-Schottky-Rectifier-Diode-30V-3-5A-0-35-Vf-smpsu_W0QQitemZ270149488699QQihZ017QQcategoryZ36332QQrdZ1QQssPageNameZWD1VQQ_trksidZp1638.m118.l1247QQcmdZViewItem

datasheet is here

http://pdfdata.datasheetsite.com/pdf1/IR/30WQ03FN.pdf

miles
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marijuana vaporizer

As Dippy explains, its Current vs Volt Drop.

Some higher current rated Schottkys, when used on a low current have much lower voltage drops - just like the data Dippy Shows - look at the BATxx spec sheets for higher current devices.

The BAT85 is described as a SIGNAL diode when all is said and done.

Looks good. You won't do much better at that price.

I've just been using SR504 0.36v @ 1amp approx and 0.5V @ 5amps Bit more expensive, I needed them for a SMPSu.

Or, if you've got a pile of BAT85s gathering dust then 2 or 3 in parallel may be OK.

Thanks for everyones input. I was totally unaware that the voltage drop through the diode increased as current increased.

I have a battery powered device that I want to reverse polarity protect in case batteries are inserted the wrong way around.

Brendan: To avoid ANY voltage drop you can always CLEARLY mark the battery insertion slots, or arrange terminals/baffles that prevent wrong way battery insertion. FWIW beefy Schottky diodes are in most cheapo solar garden lamps, so just crack one apart. Stan

... but don't let your neighbour spot you in his garden.

You can also use a N-channel or P-channel MOSFET to do this.

http://www.siliconchip.com.au/cms/A_104062/article.html

ylp88

Don't worry Dippy I wear a balaclava when creeping around other people yards at night........

Thanks ylp88 I'm printing out the article now, much appreciated for the tip.

I hear what your saying Stan, Im concernd though that if I don't make it 'idiot proof' inevitably someone will stuff it up.

Anyone can be an idiot. I managed to reverse the batteries in my cordless mouse just last night Luckily, that one is foolproof, unless I can find another way....

There' s also whats known as crowbar protection, was (maybe still is, try not to get involved with it these days) used a lot in car audio systems,
Put a diode reverse biased across the power input leads (1N4004's were commonly used) if the supply is reversed the current is shunted through the diode, therefore only 0.6 -0.8 is generaly presented to the circuit, which is usually around the spec most cct's can handle in reverse!
These cct's were usually fused and this action blew the fuse and usually the diode fused into a short cct, but this was 12v with virtually unlimited current (well at least until all the insulation fell of the wires and everthing joined together)

The advantage of this style of protection is that there's no voltage drop.

The disadvantage is that it requires a soldering iron to reset it, although with batteries (depending on type and breed) you may get away with this

The other method which is zero volt drop is to fit the diode ACROSS the power supply with an in-line fuse. If the supply is reversed, the diode conducts and the fuse blows. It's known in the industry as an "idiot diode" because the diode itself blows when the "idiot" keeps replacing the fuse with bigger and bigger ones until the diode itself melts.
Nearly all car radios use this method and nearly all "warranty" claims have blown "idiot diodes". Hmm....

@Dippy. PM box full. Will clear it tonight and get back to you.

Sorry Peter, that's what happens when you start a reply and get distracted before submitting an hour later.

Umm yes I can hear an echo

quite common on this forum...forum....forum.

BB: Cheers. No urgency.