I thought it was powering a linear regulator? The minimum voltage due to the ripple just needs to be high enough to avoid the drop-out region. Huge capacitors result in a massive inrush current, which can cause other problems.
I'm having a bit of a confusion/epiphany right now - does that mean, that the linear regulator would be able to "regulate out" that 50 Hz ripple as long as the input voltage doesn't go below the dropout voltage? Thinking about it, it seems very logical to me for the regulator (two BD139/TIP3055 pairs in this case) to be at least as fast as 50 Hz. That would mean, I was doing it wrong all the time, lol.
I have an equation here:
Ripple Voltage = Max Current / Capacitance [F]
If my transformer voltage is 18VAC * 1,414 (in fact it is 27V even under load, measured, don't know why), even 8V ripple (is that peak to peak?) should work ok, which would be only 5000uF of capacitance needed instead of 20000uF. Is that possible?
Then use an ideal diode controller designed for one MOSFET, for the fifth diode.
Didn't know such a thing exists, will have to search. Thanks for the hint (you don't know one, by accident?).
As long as the case isn't in direct contact with the diodes, I don't see how that's an issue.
Well like I said, general heatup within the case, temperature drift of all the precision devices, and so on made my concerns... Also, temperature was still rising, the 100°C i had reached only after a couple of minutes. I just didn't want to deal with that kind of heat on the diodes anymore.
It sounds like the Shottky didoes didn't have a high enough current rating. The reason why I'm questioning the need for a low loss rectifier is, it's driving a linear regulator and all you're doing is moving the heat there. The main advantage is it will work with a lower transformer voltage, but if it's already more than high enough, it won't make any difference.
I was using these and I just realized they weren't Schottkys, sorry for that misinformation:
https://www.mouser.at/datasheet/2/427/vs-16edu06-m3-1769326.pdfHowever I remember searching for diodes with lower Vf but if I recall correctly, they were all around at least 0.6V or so, when it came to currents around 4A.
But you are of course very right about "only moving the heat to the linear regulator", I wasn't looking at this from that point of view. On the upside is that I have a large heatsink plus a fan on the dual darlington pair so I have no issues of getting rid of the heat there. Also, I was thinking about lowering the transformer voltage (18VAC transformer output vs. 16VDC PSU output, which is not good) to reduce dissipation in the first place or at least raise the output voltage of the PSU, as ~16VAC transformers don't seem to be common, at least not with that kind of amperage rating. That lowers my tolerance on voltage drop on the rectifier in any case.