Low Vf diode - Page 1
Forum section: electronics / general

author: Robaroni
author_rank: Frequent Contributor
timestamp: June 21, 2016, 01:29:31 pm
content: Hi,I'm looking for a smaller SMD low Vf diode. I use the MBRA340T which is very good but a bit large for my lower current apps and the venerable 5817/19 for thru hole but I'm looking for something in a smaller package that will work for my under .5 amp apps.Thanks for the help,Rob

author: chris_leyson
author_rank: Super Contributor
timestamp: June 21, 2016, 01:47:06 pm
content: Hi Rob, I've just designed some MBR0520 Schottkeys' into a product, think they are available in higher voltages as well, MBR0540, MBR0560 etc.

author: klr5205
author_rank: Regular Contributor
timestamp: June 21, 2016, 01:49:52 pm
content: Apologies if you already know this, but websites like digikey and mouser let you sort by forward voltage if you click the little arrows at the top of a column.Just select your "must-have" parameters and then choose from the results w/ the lowest Vf.I agree with Chris though that the MBR series are a good place to start. I've used them in several products myself.

author: dannyf
author_rank: Super Contributor
timestamp: June 21, 2016, 02:05:37 pm
content: Germanium diodes have lot Vf.Alternatively, you can parallel them to further reduce Vf.

author: ocw
author_rank: Regular Contributor
timestamp: June 21, 2016, 02:34:29 pm
content: Here are some lower Vf SMD diodes that I have and use:DIODE PIV A Vf 50ma Vf .4A Vf 1A Vf 3APMEG3050EP 30 5 0.16V 0.218V 0.242V 0.288VPMEG3020EP 30 2 0.19 0.24 0.28DB2141200L 40 1.5 0.23 0.31SS14-E3/61T 40 1 0.26 0.35SD0805S020S1 20 1 0.29 0.42 0.44MSS2P2M3/89A 20 2 0.31 0.38 0.44

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 21, 2016, 05:34:38 pm
content: Schottkys haven't improved much in the last four decades. Physics is physics, and the properties of silicon haven't magically changed since then.I'm pretty happy with the specs of most PMEG parts. They're about the same improvement over standard B340 etc. kinds, as those are above the old 1N58xx kinds.Which is to say, only about a tenth of a volt Vf.It's really not much, and if you're worried about that little of a difference, you have much, much bigger problems to worry about. Consider a synchronous rectifier instead. That can get your voltage drop arbitrarily low (Rds(on) of a MOSFET), but requires a well timed synchronous gate drive signal, or a controller chip that causes delay; effectively, reverse recovery loss by a more convoluted method.If switching loss and junction capacitance is a big deal, junction diodes can still be a net win, even at fairly low voltages (>20V?). Snubber diodes often win this way, despite the other drawbacks of junction diodes.Tim

author: chris_leyson
author_rank: Super Contributor
timestamp: June 21, 2016, 08:07:30 pm
content: Quote,QuoteYep been there, what the hell, the power is flowing the wrong wayyou have to sense the diode current . Sometimes when you've got the wrong topology or controller chip and the extra electronics needed to get the synchronous gate drive just right won't fit, you have to think "I'll stick with a Schottky".

author: Robaroni
author_rank: Frequent Contributor
timestamp: June 22, 2016, 12:46:54 am
content: Thanks for all the great answers and lively discourse, always a plus on EEVblog!Linear makes a great "ideal diode", the LTC4357. I do use it when I'm over 9 volts input. Most of the time I just need a schottky, that's why I was looking for numbers on SMD devices. Thanks for the tip to look up parts using Vf, I forgot about that!Rob

author: georges80
author_rank: Frequent Contributor
timestamp: June 22, 2016, 05:43:49 am
content: CRS08 is a pretty decent schottky w.r.t. Vf.cheers,george.

author: Jeroen3
author_rank: Super Contributor
timestamp: June 22, 2016, 09:12:06 am
content: Quote from: ocw on June 21, 2016, 02:34:29 pmUse monospaced fonts next time.Code:Note that low Vf often comes high Ir.I've used theRSX101M-30TRfor low Vf andBAS116H,115for low Ir. Both SOD-123.

author: Robaroni
author_rank: Frequent Contributor
timestamp: June 23, 2016, 01:12:29 pm
content: Quote from: Jeroen3 on June 22, 2016, 09:12:06 amThe RSX101M-30TR is NRND now.Rob

author: Jeroen3
author_rank: Super Contributor
timestamp: June 23, 2016, 01:29:17 pm
content: Diodes never have a long markey life. They are always binned, and when they switch fab, they eol them all, do a +1 of the type number, and start selling again.It's not even an issue at my quantities.QuoteThe direct replacment is the RSX101MM-30, a +M in this case.

author: Robaroni
author_rank: Frequent Contributor
timestamp: June 23, 2016, 01:34:36 pm
content: Quote from: Jeroen3 on June 23, 2016, 01:29:17 pmGreat! Thanks for the help.Rob

author: batteksystem
author_rank: Regular Contributor
timestamp: June 26, 2016, 02:51:25 pm
content: Quote from: blueskull on June 21, 2016, 02:55:13 pmSilicon Carbide is for very high voltage application?