Bridge rectifier recommendation - Page 1
Forum section: electronics / projects

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: May 11, 2017, 07:21:55 am
content: Hiwe are designing a power supply, we have selected all the power transistors and diodes to be D2PACK, so we could easily mount the whole power devices to the heatsink. the problem is that it seems I can not find the suitable bridge rectifier with 500V above and 10A+ that has the same height as the D2PACK parts. do you recommend any part number?

author: tautech
author_rank: Super Contributor
timestamp: May 11, 2017, 07:40:46 am
content: Think about it.............All the power has to pass through the bridge, yes all and with silicon diode Vf losses that at 50 or 60 Hz totals up to be quite a few watts. Make it out of individual diodes if you want/need low profile and use trace width and/or thickness to conduct the heat away.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: May 11, 2017, 08:10:53 am
content: Do you know Common cathode and common anode dual D2PACK diodes with that rating in mind?

author: mariush
author_rank: Super Contributor
timestamp: May 11, 2017, 09:53:41 am
content: Just go on Digikey / Farnell / Mouser and select surface mounted diodes and then look at DPAK diodes or other surface mounted diode packages that are under ~ 2.4 mm tall (as that seems to be the DPAK package height.I assume you're also going to use some thermal pad of some sorts between heatsink and the parts, if you're going to use some heatsink, so that pad if it's thick enough would cover the minute differences of 0.1-0.3mm in height, or something like that.You could go with single diodes as well, and optionally put two of them in parallel instead of just one, to reduce current on each diode (for lower foward voltage drop) and to increase surface area (to spread heat better).here's some links .. diode arrays (common cathode, common anode, independent diodes in a package , basically multiple diodes on a chip ) :https://www.digikey.com/products/en/discrete-semiconductor-products/diodes-rectifiers-arrays/286separate single diodes :https://www.digikey.com/products/en/discrete-semiconductor-products/diodes-rectifiers-single/280Another potential solution you may have would be to have a cutout in the circuit board and have the bridge rectifier package sit in that cut out rectangle with just the leads soldered to the circuit board. On one hand, you get an extra mm or so (the pcb thickness) but usually cutouts on circuit boards make them more expensive to make, and you'd have to keep in mind that now you may heat up the other side as well (where the pcb is screwed onto the case, and if the product is somewhere where there's vibrations and shocks, the rectifier shouldn't be loose in the cutout, hanging just on the leads soldered to the board, as they may break in time. Would also be hard to install on pcb with a machine, it would probably be an extra manual step to solder it.

author: w2aew
author_rank: Super Contributor
timestamp: May 11, 2017, 04:39:23 pm
content: Quote from: mariush on May 11, 2017, 09:53:41 amParalleling diodes to spread out the heat and lower Vf is a not a good idea. Silicon diodes have a negative temperature coefficient. Thus, as they heat up, the Vf goes down. The diodes will never be perfectly matched. Thus, from the beginning, one of the two will take more current that the other, and it will heat up slight more than the other. In doing so, it's Vf will drop more than the other, causing it to draw more current, get hotter, etc. In the end, one diode will take the bulk of the current and make most of the heat - defeating the purpose of paralleling in the first place.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 11, 2017, 04:45:48 pm
content: Just so save you from the major headache later:You have fallen into the trap of doing the beginner mistake of trying to cool DPAK/D2PAK devices through the plastic.The additional cooling through the plastic to the heatsink will be very minimal, expect something like 10-30% increase in cooling compared to no heatsink at all. This is because the plastic is very thick and doesn't conduct much heat; these devices are not designed to be cooled that way. The thermal resistance through the plastic isn't typically even specified, so you can't do the analysis without prototype measurements, but the results I've seen are typically poor.The proper way to do it is by using a bunch of thermal vias (if you throw some extra money in PCB manufacturing, you can even get them filled with copper) - maybe something like 15-20 0.6mm vias - very close to the tab of the device, then use a SILPAD with good thermal conductivity (check the spec) on the opposite side to transfer the heat to the heatsink.Do some thermal calculations. There are online javascript calculators that can calculate the thermal conductivity of plated vias for you.Paralleling diodes works when the extras are cheap, you have the real estate for them, and you can thermally couple them, and you derate the summed current rating considerably; i.e., by paralleling two, you don't expect 200%I, but maybe 120%I, or if really well thermally coupled, maybe 150%I.

author: jbb
author_rank: Super Contributor
timestamp: May 12, 2017, 06:15:34 am
content: You can try TO-220 / TO-247 devices bent 90 degrees, and put holes in the board so you can poke a screwdriver through to fix them to the heatsink.This gives good compactness and thermal capability (used in many PV inverters) but makes assembly quite hard. And repair quite hard. And attaching scope probes quite hard.

author: oldway
author_rank: Super Contributor
timestamp: May 13, 2017, 06:31:45 am
content: Use an aluminium backed PCB for better cooling of DPAK....http://www.pwcircuits.co.uk/ims.html