A Simple Adjustable DC-DC Converter, or a DIY Bench Power Supply V2.

Many of you probably remember my saga of building a DIY bench power supply.
But I've been asked more than once for something similar, only simpler and cheaper.
In this review, I decided to show an alternative version of a simple adjustable power supply.
Come on in—I hope you'll find it interesting.

I kept putting off this review—sometimes I didn't have the time, sometimes I wasn't in the mood—but I've finally gotten around to it.
This power supply has somewhat different specs from the previous one.
At its heart is a digitally controlled DC-DC step-down converter board.
But all in good time. For now, here are a few standard photos.
The board arrived in a small box, not much bigger than a pack of cigarettes.


Inside, in two bags (bubble wrap and an antistatic bag), was the star of this review: the converter board.


The board has a fairly simple design: a power stage and a small board with a processor (this board looks similar to one used in another, lower-power converter), control buttons, and a display.


Board specifications:
Input voltage: 6–32 V
Output voltage: 0–30 V
Output current: 0–8 A
Minimum voltage setting/display resolution: 0.01 V
Minimum current setting/display resolution: 0.001 A
The board can also measure the capacity delivered to the load, as well as power.
The switching frequency is listed as 150 kHz in the manual, 300 kHz in the controller datasheet, and about 270 kHz by my measurement—which is much closer to the datasheet figure.

The main board carries the power components, PWM controller, power diode and inductor, filter capacitors (470 µF × 50 V), a PWM controller for powering the logic and op-amps, op-amps, a current shunt, and input and output terminals.


There's practically nothing on the back, just a few high-current traces.


The auxiliary board has a processor, logic ICs, a 3.3 V regulator to power the board, a display, and control buttons.
Processor: 8s003f3p6
Logic: 2 × 74hc595d
Voltage regulator: 1117-3.3


The power board has two mcp6002i operational amplifiers (the ZXY60xx uses the same op-amps)
The PWM controller for the board's own power supply is an xl1509 adj


The power-stage PWM controller is an xl4012e1 chip. According to the datasheet, it's a 12 A PWM controller, so it isn't being pushed to its limits here, which is reassuring. However, keep in mind that exceeding the input voltage can be dangerous.
The board description specifies a maximum input voltage of 32 V; the controller's absolute maximum is 35 V.
More powerful converters use a low-current controller to drive a high-power MOSFET. Here, a single high-power PWM controller does it all.
Sorry about the photos; I just couldn't get them to come out well.


The power diode assembly is an mbr1060


While inspecting the board, I noticed a repaired trace. I don't think it's anything to worry about.
But it does show that the manufacturer at least powers the boards up for testing.


When first powered on, the board displays the default setting of 5 V.


The current is set to 1 A as well. These settings can be changed.
To do this, in this mode set the desired current and press SET. The display will show four dashes; then repeat the process for the voltage.
After power-up, the board will start with these settings.
You can also configure the output to turn on automatically and have the display alternate automatically between current and voltage.


The output voltage is set quite accurately…


The current readings are somewhat worse, but I don't think it's a big deal.


As the voltage increases, the error gets larger.


The current setting accuracy, however, remains practically unchanged.


As a test, I connected an automotive bulb and set the voltage to 13.5 V




The board description says that natural cooling is sufficient for load currents up to 6 A, while currents above 6 A require active cooling.
I checked the temperature at a current of 6 A and a load voltage of about 12 V.
After 20 minutes of warm-up, the temperatures were as follows: PWM controller — 82 degrees.
Output diode assembly — 72 degrees
Power inductor — 60 degrees.

In principle, 6 A with passive cooling seems quite plausible, but the board was tested on the bench. If you install it in an enclosure, it's better to use active cooling or limit the current to at least 5 A.

And with that, we've smoothly moved on to the practical part of the review :)

I uploaded descriptions of the components used, as well as the instructions, as an archive.

The instructions I found online describe how to enter service mode, where you can change some settings. To enter service mode, power up the board while holding down the OK button. The numbers 0–2 will appear on the display in sequence. To change a setting, release the button while the corresponding number is displayed.
0 — Enable automatic output voltage when power is applied to the board.
1 — Enable extended mode, which displays not only current and voltage, but also the capacity delivered to the load and output power.
2 — Automatically cycle through the measurements on the display, or select them manually.

The instructions also give an example of saving settings. The board lets you set current and voltage limits and has a settings memory, but I didn't dig into that any further.
I also didn't try the UART connector pins on the board, because even if they do anything, I couldn't find any software for this board anyway.

Summary.
Pros.
1. Quite a range of features: setting and measuring current and voltage, measuring capacity and power, and an automatic output voltage mode.
2. The output voltage and current ranges are quite sufficient for most hobbyist applications.
3. The build quality isn't exactly great, but there are no obvious flaws.
4. The components are generously rated: a 12 A PWM controller where 8 A is specified, and 50 V capacitors on the input and output, despite the specified 32 V.

Cons
1. The display is very inconvenient: it can show only one parameter at a time, for example—
0.000 — Current
00.00 — Voltage
Р00.0 — Power
С00.0 — Capacity.
For the last two parameters, the decimal point floats.
2. As a result of the first point, the controls are rather awkward. A rotary encoder would have helped a lot.

My opinion.
It's a decent board for building a simple adjustable power supply, but it's better and easier to use a ready-made power supply.

This board was provided to me free of charge by the Gearbest store for testing and review.

This is my fiftieth review, almost a milestone (how did I manage to write so many?). I hope it's useful and interesting. Post your questions in the comments and I'll try to answer them.