Diode characteristics - Page 1
Forum section: electronics / projects

author: TreeOone
author_rank: Newbie
timestamp: May 24, 2019, 07:10:48 pm
content: Hi!Can somebody please explain why two apparently similar diode bridges have 100% difference in price?I am talking about VS-UFH60BA65, found here:https://www.digikey.com/product-detail/en/vishay-semiconductor-diodes-division/VS-UFH60BA65/VS-UFH60BA65GI-ND/9477549Datasheet:https://www.vishay.com/docs/96135/vs-ufh60ba65.pdf….and VS-SA61BA60, found here:https://www.digikey.com/product-detail/en/vishay-semiconductor-diodes-division/VS-SA61BA60/VS-SA61BA60-ND/4932492Datasheet:http://www.vishay.com/docs/94688/vs-sa61ba60.pdfIt even seems that VS-UFH60BA65 should have higher price, because it has shorter recovery time, and higher reverse voltage.The only visible difference is junction temperature, which I don’t fully understand. It says VS-SA61BA60 has maximum DC output current at much lower case temperature 57C, versus VS-UFH60BA65 at 123C. Does this means you have to cool VS-SA61BA60 much better than VS-UFH60BA65 for the same 60A current? Dissipation in Watts per each amp are similar.What is the reason of 100% price difference?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 24, 2019, 07:30:31 pm
content: Easy, the first one you can buy in quantities as small as 1. The second one you have to buy at least 160 of 'em!

author: TreeOone
author_rank: Newbie
timestamp: May 24, 2019, 07:36:20 pm
content: More you buy, more you pay for each piece?Not sure about that:https://eu.mouser.com/ProductDetail/Vishay/VS-UFH60BA65?qs=MLItCLRbWswxkbkHYft7VA%3D%3Dhttps://eu.mouser.com/ProductDetail/Vishay-Semiconductors/VS-SA61BA60?qs=lgjwDzixuo3EwlaH8ytO%252Bg%3D%3D

author: Zero999
author_rank: Super Contributor
timestamp: May 24, 2019, 08:51:49 pm
content: The cheaper one has a higher on voltage.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 25, 2019, 05:22:13 pm
content: Quote from: Conrad Hoffman on May 24, 2019, 07:30:31 pmActually, that works against it, the one beinghalf the costof the one you have to special-order 160 of.More likely they were never very good at making the costlier one in the first place, or it's on NRND and so the price is jacking up to reflect the shrinking supply and reluctance to produce more.But quantity, and supplier markup, is, in general, the biggest part of the cost and variance you will see at small quantities.You don't really have representative pricing until you get into the thousands for power devices, or millions for small chips (resistors etc.). Basically, whole pallets at a time. Even then, prices are negotiable in those quantities. At all levels, from manufacturer to distributor to broker.Quantity may vary; TI doesn't give a shit about a thousand here or there, but ADI does. I once met with an ADI FAE and got a nice price on a quad ADC that undercut the competing NS/TI dual ADC (per part in fact, making it a good deal indeed), and that for quantity under 1k/yr. (The FAE then forwarded the negotiated price to the supplier, DK I think, for future purchasing. You won't get factory-direct unless you're using millions qty.)Cost need not reflect capability. For semiconductors, one of the biggest costs is making the masks themselves. Once those are written off, the cost drops to mere production cost, of which the package itself is often dominant. For example, the cheapest TO-220 you may find is a fraction of a buck, and the cheapest TO-247 is a buck and a half, even with the same silicon inside both. And the amount of silicon inside both is a tiny square not much bigger than a classic 2N2222 die, say.The SOT-227 I don't think gets much below $10, that's about your starting point for those parts.As die sizes shrink and capabilities continue to improve, costs can remain competitive, even against classic parts that are very cheap on the global market.Tim

author: TreeOone
author_rank: Newbie
timestamp: May 27, 2019, 09:38:48 pm
content: Tnx T3sl4co1l for your elaborate explanation.So the general conclusion is the price is not reliable measure of electronic component’s usefulness/value at low quantities.One other matter bugs me in the end.Would somebody comment the difference in maximum DC output current at specified case temperature? VS-SA61BA60’s rated current is specified at much lower case temperature Tc.What can be deduced from low or high case temperature at rated current? Both diode bridges have similar losses per each Amp they pass through.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 27, 2019, 09:44:07 pm
content: Something about die attach I would guess.Tim