Multichannel DC-DC Converter Pico PSU ATX and a Little About How to Use It

I understand that writing about a converter like this now is a bit like reviewing a steam locomotive pipe: interesting, but nobody needs it.
But I figured that if I needed one, it might come in handy for someone else too.

I ordered this converter during the August 25 sale, tested it as soon as it arrived, confirmed receipt, then tossed it in a drawer and didn't think about it again for several months.
But I finally got around to this board too. Below is a description of the board and a little about how to use it.

As I mentioned in the title, I got it during a sale for ten and a half bucks. I'd been thinking about buying one for a long time, and then I saw a pretty good price, so I ordered it.
I was surprised that the seller shipped it with tracking. Lately, sellers seem to be cutting costs more often.
It arrived in a fairly neat little box, and was also packed in an antistatic bag. It gets 5 out of 5 for appearance.

The package consists of a small board and a cable with connectors.


Specifications from the seller's page.


Since there are no instructions or anything else in the package, I'll go straight to the board.
This board has already been reviewed by others, so I probably won't have anything new to say about it. There's also plenty written about it online.


The design consists of a standard 24-pin ATX power connector and a board soldered directly to its pins.
The board has a connector for additional cables, as well as a separate power connector for the board itself.
Large components are mounted on one side: a pair of inductors and four capacitors.


The description claims a whopping 160 W. In reality, it's much simpler than that.
In fact, if you calculate the power from the specifications table, you get about 80 W.
But that's not the whole story. If you look more closely at the device's block diagram, it's clear that the 12 V rail passes straight through, and the output current on this rail is limited only by the capabilities of the transistor that switches it.
The converter's actual power is (5x5)+(3.3x5)+(5x1)+(12x0.03)= 47 W.
The 12 V output is switched by a transistor.
The standby 5 V is provided by an additional regulator that is always on.
The 3.3, 5.0, and -12 V rails turn on together with the 12 V rail.
There's also a separate IC that generates a signal indicating that all the voltages are within spec.


The inductors are very compact, but still quite well made.
Two types of capacitors are used: 100 µF 16 V and 150 µF 10 V.
Presumably, the first two are on the board's power input, and the other two are on the 5 and 3.3 V rails.


The inductors are made in an unusual way compared with those on cheap converter boards.
The winding uses flat wire rather than ordinary round wire.
In switching transformers that operate at high currents, the winding is sometimes made from thick foil, which can noticeably improve performance and reduce losses.
A similar principle is used here.


The other side of the board, on the other hand, is packed to the brim, with a very high component density.
All the PWM controllers and power transistors are located here.


1, At the heart of the board is a dual-channel ISL6440IAZ converter with synchronous rectifier control, which can also generate a PG (Power Good) signal.
2. There is also an inductor for the 5 V standby converter on the underside of the board, presumably, since I couldn't find any other use for it. :)
Interestingly, I didn't see a PWM controller generating this 5 V output. Perhaps it's somehow tied to the main PWM controller.
Four MOSFETs for the converter are located nearby; the first PWM controller channel definitely controls two of them.
3. Another pair of transistors for the second converter channel.
4. Power monitor. WT751002, this IC monitors the output voltages and generates the PG (Power Good) signal, which is then sent to the computer's motherboard. Most likely, the main PWM controller's PG signal wasn't used. It's a little unclear why, but the designers presumably had their reasons.


A little about the PWM controller used here.
The original datasheet shows a circuit for 1.8 V and 3.3 V outputs; in this version, it provides 3.3 V and 5 V.


The PWM controller's circuit design supports synchronous rectification.
This approach can noticeably improve the converter's efficiency.
A standard DC-DC converter—in this case, a step-down converter—uses a transistor, a diode, and an inductor.
In a synchronous rectifier design, a MOSFET is connected in parallel with the diode and turns on during the time the diode would otherwise conduct.
This approach is used in multiphase PWM controllers on motherboards and elsewhere. It's a shame that so few simple PWM controllers support this feature.

The diagram shows the difference between a conventional converter and one with synchronous rectification.
Don't be confused by the switch representing the transistor being connected in parallel with the diode, while the diagram above has no diode. The diode is built into the MOSFET. Technically, it's a side effect, but one that can sometimes be put to good use.


The complete list of ICs and transistors installed on the board.
isl6440 - dual-channel PWM controller
WT751002 — power monitor, Power Good signal generator.
FDS6679AZ — P-channel MOSFET, -30 V, -13 A, 9 mΩ
AP4438CG — N-channel MOSFET, 30 V, 11.8 A, 11.5 mΩ.
AP92U03GM — N-channel MOSFET, 30 V, 90 A, 4 mΩ.

All the datasheets in one archive, in case they're useful.

The kit included a cable that plugs into the converter board at one end, while the other end has three connectors: one for additional motherboard power and two for connecting hard drives or CD/DVD drives.
Power is supplied to the board through a standard 5.5 mm connector on a cable. This is usually done so the connector can be mounted on the back panel of the device and connected to a power supply with a standard plug.


That should be enough about the board for now. Let's move on to what I bought it for.
I wanted to upgrade an old computer. It works fine; inside, it has a modified ATX power supply, a motherboard with an Atom processor, and 2 GB of RAM.
I plan to use it as a replacement for an even older computer that serves as a mini server. That one is built around a D201GLY2 motherboard with a Celeron 220 processor and 1 GB of RAM.

The power supply already installed is pretty good—I'd even say excellent. It's a 145 W Astec, but I can't fit two hard drives with it :(


Out of curiosity, I measured how much power the computer draws with the converter board installed: about 25 W.


Along with the converter board, I also used the power supply board, which I already reviewed.


I did decide to make a few changes to the power supply board, though.

Further details on using the converter board.

So, this is the little mini-computer I ended up with—or, more accurately, a file server.
It still needs some work, and it looks pretty makeshift, but it works, and works quite well. I just need to sort out the fan issue.
There are three buttons on the front panel. The large one works as usual, as the power button; the two smaller ones reset the computer when pressed together. I also wired up the two original LEDs: green for power, red for the hard drive.


The back has the usual connectors. I especially needed the COM port, since I have a Dallas temperature sensor connected to monitor the temperature where the computer is installed.


So, to sum up.
Pros
The converter works perfectly.
It does get warm, but stays within acceptable limits.
No complaints about shipping or packaging.
Low price.

Cons
The only thing I can think of is that the wires to the hard drives and motherboard are a bit thin.

My take: I like the board. I was worried that running two hard drives would cause problems (the load on the 5 V rail goes up), but everything worked out great. The power supply does make a slight whining noise in standby, but since the computer runs 24/7, that wasn't a big deal for me. Of course, this setup already seems outdated, but with this converter, a power supply, a mini-ITX board, a couple of hard drives, and a satellite receiver case, you can build a small NAS. Even 5400 RPM drives are more than fast enough.
The old computer had a 100 Mbps network card; the new one has a gigabit card, though I doubt I'll make much use of it.
So far, everything is great, except that I need to come up with better cooling, since hot weather could cause problems.

I hope you found this review interesting. I look forward to your questions and suggestions in the comments.