Electronics > Projects, Designs, and Technical Stuff
Trouble finding non-schottky SMD power diode
Circlotron:
Plenty of TVS diodes come in SMC / DO-214AB size. Their forward characteristics may be suitable.
MustardMan:
--- Quote ---Modern rcds use electronics, with a capacitive dropper low voltage supply, and don't power the trip device direct from the ct output
--- End quote ---
Yeah - I bought one yesterday & pulled it apart this-morning. Very disappointing. A sense CT and some electronics. Despite the complication & added parts, I suppose that makes it cheaper because then all trip ratings simply use the same guts with a different trigger setting. Oh, for the good old days when such things were made with just a CT and a solenoid.
It might be still worth looking at, but I am now leaning back towards a silicon solution
I am not so constrained by height, so I can use TO220 style devices with a caveat of two. Any more and it just starts taking up too much space.
MOSFETs (back-to-back, using them only for their body diodes)... there are some reasonably priced ones out there, and the curves look nice and steep (eg: attached, 0.6v at 10mA at 25C). Extra circuitry to drive the gate for lower dissipation at higher currents will unfortunately not fly because of the additional space required.
SiC rectifiers have much higher Vf (eg: attached, 0.7v at 10mA at 25c) as do the body diodes in SiC FETs, and the curves are good until low amps. I could go higher current ratings to get the curves steeper for longer, but I thought the prices for the 'smaller' SiC devices were high - until I saw the prices for the 'larger' SiC devices!
Thanks to all the respondents for the ideas you have given me!
Cheers, MM.
MustardMan:
:palm:
Somewhat goose-like, he realises that a fairly simple way of determining if a diode is schottky or silicon is Trr, as there is no Trr with a schottky!
Very few manufacturers put data on their spec sheets that cover any sort of decent range (thanks to Diodes Incorporated for putting the time into doing a decent test on this device) and this curve shows the behaviour at low currents. I had initially wondered why there were extra bends at Tj=25 and Tj=-65... which is of course the diode knee. It is very likely that other diodes with a Trr (ie: PN junction diodes) perform the same.
I do find it interesting though that just before the 25C 'knee' the forward voltage is in the vicinity of 0.5 volts. I always thought a PN junction at 25C was 0.7 volts?
MM.
Circlotron:
Why do semiconductor manufacturers draw diode graphs like that? Usually you want to know the unknown forward voltage drop at a known current, so the current (the independent variable) should be across the bottom and the voltage drop (the dependent variable) should be up the side! I can’t think of a case where you would apply a certain voltage to a diode and need to know what the resulting current is.
Zoli:
--- Quote from: MustardMan on August 19, 2020, 12:18:33 pm ---Hi All,
I am having great difficulty finding a surface mount (preferably SMC package) power diode that is not schottky. I have a specialised application that requires the voltage drop present across a silicon PN junction (ie: 0.7 volts), but it seems that pretty much every manufacturer has gone schottky because of the lower Vf.
...
--- End quote ---
So, let's see what kind of options Digikey(just because is the most popular supplier 'round) has, when selecting diodes:
Surface mount: yes, is present
Voltage - Forward(VfMax): surprisingly, this one is present, too
Current - Average rectified(Io): this one get booooring...
So let's go, and see, what is available - but I think, you should do it for yourself.
Anyway, this post is not intended to "teach you a lesson"; the intentions are to give you some guidelines for the future - and thank you for reading it.
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