I'm building John Broskie's Aikido All-in-One 9-pin line stage. The heater power supply asks for a pair of MUR410G rectifier diodes. Unfortunately, these do not seem to be available at the moment.
https://www.mouser.ca/ProductDetail/onsemi/MUR410G?qs=Gev%2BmEvV0iaM6cmMeVpMTQ==
Can anyone suggest an alternative part? I'm guessing something like this would work, but I'd like confirmation since I don't really understand this solid state stuff.
https://www.mouser.ca/ProductDetail/Diodes-Incorporated/MUR460-T?qs=Znm5pLBrcAJfuPDOuoQZ/Q==
The schematic is provided below.
https://www.mouser.ca/ProductDetail/onsemi/MUR410G?qs=Gev%2BmEvV0iaM6cmMeVpMTQ==
Can anyone suggest an alternative part? I'm guessing something like this would work, but I'd like confirmation since I don't really understand this solid state stuff.
https://www.mouser.ca/ProductDetail/Diodes-Incorporated/MUR460-T?qs=Znm5pLBrcAJfuPDOuoQZ/Q==
The schematic is provided below.
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Mostly for my education: Is there a reason the MUR460-T I mentioned in the first post won't work? If so, why?
No reason it won’t work. But higher voltage versions cost more and have a higher forward voltage drop at the same current. Not that it matters much in this application, where it’s just there for reverse polarity protection. In applications where it carries operating current, Vf directly impacts efficiency.
If it's just there for reverse polarity protection, a slower recovery diode like the 1N5401 would work just fine, and likely have a higher surge current rating than the faster MUR part.
Yes, one would hope that the regulator could tolerate output exceeding input for a microsecond or two while the current in the diode waits to go into conduction. They certainly don’t like the energy of a big cap being fed back and that’s why the diodes are there. I suppose if the regulator chip is sensitive enough to reverse polarity a faster diode might be required. I know the old 7800 series and the 317 can just go with a 1N400x.
A Schottky diode would also be an interesting choice for a protection diode. An SB5100 will handle 150A of surge current.
With only 1000 uF of output cap at 12V that’s probably overkill. Somebody goes and sticks 20,000 on there and yeah, you’ve got to feel for the poor diode.
I am careful of what cap I put on the output of a regulator. I have seen large output caps causing oscillation with 3-terminal regulators. 100-200uF is more than enough.
They don’t like caps too big or too small. There is usually a range in the tens of nanofarads that send them off singing, and the 1 to 10 uf that usually used swamps it out. It’s a major problem with regulators used for powering RF amplifiers. The cap that stabilizes the amplifier makes the regulator go stupid. Can’t win.