Diodes in parallel is bad, one will do all the work the other will do nothing.
re-read my own post, my english sucks.... on was supposed to be 'one' and two was supposed to be 'to'. Cheers mates!!
It can be done but in most cases shouldn't.
With diodes available into the thousands of amps where is the need to parallel a pair or more? ST says in their literature it is common in power electronics??? I have never serviced any unit built that way. I can assure you in the 4400hp locomotives where I design the power electronics I have never used diodes in parallel and specifically not on the alternator 3 phase output where we use diodes pucks about 4" in diameter.
We do tons of low voltage LLC resonant converter crap and again I have never done and never seen diodes in parallel. Can it be done, sure...Should it be done, I can't think of one good reason. I do have many high voltage circuits where we use diodes in series, mostly 1N4007 type stuff and for many years used the parallel compensating resistors and small .001uf caps although these days the single piece slightly longer body high voltage diodes are more common and are a single package answer to what was a multi-package problem years ago.
To optimize the Bill Of Materials (BOM), a designer might choose to use the same component twice, thus reducing the number of different components to be purchased and handled. To avoid a dangling antenna, the designer would then connect the spare diode in parallel to the single diode.
Somewhat outside of the scope of the immediate discussion here are cases where for redundancy reasons 2 or 3 Zener diodes are in parallel, with definitely no balancing resistor allowed.
I recently repaired a circuit where two plain diodes where in parallel for safety reasons in case one failed open.
They were acting as flyback/freewheeling diode in a 230V circuit, and due to the nature of the circuit, failing open would mean the possibility of a user being exposed to the inductive voltage spikes.
What happens when two diodes are in parallel? if this is a bad idea, why exists shotkky diodes with common cathode? (i. e. to220 package).
As has been said, it all depends on how well they are matched. Heck, almost every diode on a IC will be made up out of loads of tiny diodes put in parallel. Same applies to FETs, in the end I can only make a tiny FET on chip, and to get bigger ones I have to put them in parallel, with multiple fingers.
As has been said, it all depends on how well they are matched. Heck, almost every diode on a IC will be made up out of loads of tiny diodes put in parallel. Same applies to FETs, in the end I can only make a tiny FET on chip, and to get bigger ones I have to put them in parallel, with multiple fingers.
Although modern power FETs do suffer poor linear SOA due to hotspots as a result. Just saying.
You can parallel schottky diodes, but better not PN diodes, unless they are really close that you can consider then isothermal.
Schottky diodes' internal drift region resistance will increase with temperature due to reduced carrier mobility, thus current will tend to shift to the one that is cooler, balancing the temperature.
Although modern power FETs do suffer poor linear SOA due to hotspots as a result. Just saying.
Still I see shorted Schottky diodes at the secondary side of SMPSUs with a few diodes in parallel?
What happens when two diodes are in parallel? if this is a bad idea, why exists shotkky diodes with common cathode? (i. e. to220 package).
As has been said, it all depends on how well they are matched. Heck, almost every diode on a IC will be made up out of loads of tiny diodes put in parallel. Same applies to FETs, in the end I can only make a tiny FET on chip, and to get bigger ones I have to put them in parallel, with multiple fingers.
Although modern power FETs do suffer poor linear SOA due to hotspots as a result. Just saying.
I'm no power-semiconductor guy, so I can't be sure, but isn't that more a matter of optimization? Most of those power FETs are targeted at switching applications, so linear-region SOA is not a primary concern in their design.
As has been said, it all depends on how well they are matched. Heck, almost every diode on a IC will be made up out of loads of tiny diodes put in parallel. Same applies to FETs, in the end I can only make a tiny FET on chip, and to get bigger ones I have to put them in parallel, with multiple fingers.
Although modern power FETs do suffer poor linear SOA due to hotspots as a result. Just saying.
I'm no power-semiconductor guy, so I can't be sure, but isn't that more a matter of optimization? Most of those power FETs are targeted at switching applications, so linear-region SOA is not a primary concern in their design.
Yes, I'm not sure either. As T3sl4co1l says, you can get modern devices suitable for linear operation. I guess the devil is in fine the detail. I've rather lost track since power lateral mosfets used in linear operation. They had positive temperature coefficient and so gave pretty much perfect sharing, both across the die and between devices.