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Power Supply 101 (Linear Supply)
- Thread starter DonH56
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- #45
Depends upon the application and design trades (including cost). Please take these as off-the-cuff thoughts about something not in my main area of expertise.
Diodes are cheap, reliable (mostly), simple, and the voltage drop is not a concern in many applications. Adding a diode controller like the LT4320 and using MOSFETs (or whatever active device you choose) plus supporting components (typically clamps across the controller to prevent overvoltage surges, perhaps diodes across FETs if they aren't built-in like most power FETs these days, etc.) is a more costly solution. Often significantly more costly just for components, plus the additional board area. Design is more involved since you have to match the controller's drive capability to the active devices for things like gate slewing current, and may need to add additional snubbers or other components to limit RFI from switching the gates. Gains include lower IR drop and thus less wasted energy, cooler operation of the rectifiers (less heat) and perhaps less in the way of thermal structures around the rectifiers, and more control of things like in-rush current. Over voltage/current monitoring and protection could be built into the controller (though in my very limited experience is usually a second chip).
Are there fully integrated solutions for lower-power applications? I do not know, but seems like a market exists, and then you'd have a single-chip solution. Chances are those applications are using integrated SMPS instead, however.
In any event, as far as the original topic, rectifier choice is irrelevant in showing how a conventional full-wave rectified power supply works. One of the things really neat about ASR is the high technical level of the contributors. These basic overviews of mine are mainly for lay folk, e.g. audiophiles interested in learning a bit about the stuff "behind the curtain". It'd be great to shift the detailed discussions into new threads where we could dig (much) deeper.
Interesting thought - Don
They're just being weird and difficult. I worked in the computer industry for over 40 years, and giga was never, ever pronounced like "jiga". Even in other countries.
KSTR
Major Contributor
Only when you start getting thermal and efficiency issues even with good Schottky rectifier diodes it starts to make sense using LT4320 + MOSFETS, further for split supplies you can't use center-tapped transformer, rather you need two complete independent bridge circuits on isolated dual secondaries (the LT4320 relies on exact current matching at the outputs).
This limits its useful applications to stuff like 6.3Vdc/10A tube heater supplies and such. And it does nothing for output ripple, actually ripple can increase in level and amount of higher order harmonics.
Yes, the only time I've seen that active rectification was useful was low voltage high current switchers. And frankly a lot of the recent controller ICs have the feature built in.
AnalogSteph
Major Contributor
Indeed, it's pretty much a standard feature in PC power supplies these days.
In an audio power amp supply, output voltages tend to be high enough that even the drop of standard silicon rectifiers isn't too much of a concern, and most of the losses are in the transformer anyway (typical efficiency ~80%, minus idle losses), so it doesn't make sense to chase the last bit of efficiency in the rectification department. Should the rectifier break a sweat at high currents, you can generally just put in a bigger one and/or even provide heatsinking. Thankfully, the nature of audio signals means that sustained current requirements aren't necessarily all that high in real-world use. The thing just needs to not die during adverse conditions.
Should you have acquired a superbly efficient transformer by any chance (making those seems to be an art in itself), you might consider going Schottky for the lower-voltage supply feeding line-level circuitry, but that's about it.
In an audio power amp supply, output voltages tend to be high enough that even the drop of standard silicon rectifiers isn't too much of a concern, and most of the losses are in the transformer anyway (typical efficiency ~80%, minus idle losses), so it doesn't make sense to chase the last bit of efficiency in the rectification department. Should the rectifier break a sweat at high currents, you can generally just put in a bigger one and/or even provide heatsinking. Thankfully, the nature of audio signals means that sustained current requirements aren't necessarily all that high in real-world use. The thing just needs to not die during adverse conditions.
Should you have acquired a superbly efficient transformer by any chance (making those seems to be an art in itself), you might consider going Schottky for the lower-voltage supply feeding line-level circuitry, but that's about it.
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