Everyone loves a full-wave bridge rectifier, but there’s no denying that they aren’t 100% efficient due to the diode voltage drop. Which isn’t to say that with some effort we cannot create an ideal bridge rectifier using active components, as demonstrated by [Mousa] with an active bridge circuit. This uses the NXP TEA2208T active bridge rectifier controller, along with the requisite four MOSFETs.
Taking the circuit from the datasheet, a PCB was created featuring four FDD8N50NZ MOSFETs in addition to the controller IC. These were then compared to a diode-based bridge rectifier, showing the imperfections with the latter when analyzing the output using an oscilloscope.
As expected, the active rectifier’s output was also one volt higher than the diode bridge rectifier, which is another small boost to overall efficiency. According to NXP’s product page, there’s about a 1.4% efficiency gain at 90 VAC, with the chip being promoted for high-efficiency operations. When you consider that many designs like computer PSUs feature one or more diode bridge rectifiers often strapped to heatsinks, the appeal becomes apparent. As for [Mousa], he put this particular board in his laboratory PSU instead of the diode bridge rectifier, because why not.
Perhaps the biggest impediment to using an active rectifier is the cost, with the TEA2208T coming in at $4 on DigiKey for a quantity of 100, in addition to the MOSFETs, PCB, etc. If power efficiency isn’t the goal, then some wasted power and an aluminium heatsink is definitely cheaper.
A single video by Boxxy wastes more energy than basic rectifier over its entire lifetime.
That nerd burn is so sick it heats the PCB until all components are dropping off.
(The tin fumes are a bonus sick “burn” to the nostrils.)
Not sure if there’s any substance to it but whatever.
“Perhaps the biggest impediment to using an active rectifier is the cost, with the TEA2208T coming in at $4 on DigiKey for a quantity of 100, in addition to the MOSFETs, PCB, etc.”
Any company using this can just raise their prices and say, it’s the tariffs. Problem solved.
Ok NXP, why no datasheet? No PDF with useful info, no sale. And the product would be interesting too, I would like to maybe make a bench supply with something like this. I am curious if it does SMPS active rectification.
What are you talking about? It’s linked right on the product page.
https://www.nxp.com/docs/en/data-sheet/TEA2208T.pdf
Depending on how some “ideal diodes” are implemented, they can have interesting and sometimes dramatic failure modes, like holding a switch (“diode”) closed when the source power is removed but the load power is still present (like a battery charger).
A quick perusal of the data sheet doesn’t reveal how this IC behaves in cases like that. It appears that when input AC power is removed the control circuitry turns off all the MOSFET gates, but it also looks like it requires the load voltage to disappear too in order for this to happen.
It also requires a curious 0.45-second reset period after power removal to reset and restart normally. What happens if that constraint is not satisfied, like everyday mains power glitches that remove power for a cycle or two during utility switchgear changes?
It merits some extra testing before building this into a product, especially if you’re doing something unusual like redundant or multiple supplies, battery backup, battery charging, etc.
Some pinball games flash their playfield illumination lights (connected to 6.3VAC) with a relay. I have been looking for a clickless solution without voltage drop, but it looks like a relay is still king.
You could use an SSR for that.
In the absence of details, I would think a triac is the obvious solution.
Not at 6.3V AC, Triacs have >1V voltage drop. Same goes for SCR- and Triac-based SSRs.
There are an awful lot of optorelays that will do that. For example, a TLP170 drops less than a tenth of a volt at 0.3A, for much less than a couple of bucks.
Triac or SSR would sort of work, but the voltage drop would be too much to keep 6.3V lamps at normal brightness. Maybe two anti parallel connected MOSFETs could work, but then driving them is not going to be easy.