DC-DC converter with QC 3.0 support

It's been a while since I last wrote about voltage converters, and today I'm reviewing not just a converter, but one with the added ability to work with QC 2.0 and 3.0 protocols.
This won't be a very long review, but I hope it'll be useful.


I've already published lots of reviews of converters, explaining the theory, showing practical applications, and discussing possible modifications. This time, though, I decided to keep things a bit shorter and focus only on the converter itself.

When the order arrived, I was a little surprised by the size of the packaging, especially compared with the converter itself.


The converter itself is fairly compact, about the size of a matchbox. There was a bit of excess PCB material sticking out at the side, which I snapped off later. Without it, the board measures 52x30x13 mm.


The store page lists the main specifications, which tell us that:
Input voltage: 12–36 V
Output voltage: 5.2 V
Maximum output current: 5 A
Quick Charge modes: 5/9/12 V
Typical efficiency: over 93%

The output current at 9 and 12 V is left “off camera.” Also, the input voltage range is listed as starting at 12 V, but keep in mind that this is a step-down converter, so with a 12 V input the output will be lower.


The board looks pretty good. It has a dual screw terminal at the input and a USB socket at the output.
There are four mounting holes, spaced 46x24 mm apart.


The input has a 220 µF, 50 V capacitor; the output has a 470 µF, 35 V one. The voltage ratings provide more than enough headroom. I'd have used a slightly larger capacitor on the output, but in practice it works fine as is.


Next, I'll go over the converter's main sections, but first I'll show where they are on the board to make things easier to follow.
1. Red — the voltage converter itself.
2. Yellow — the QC 2.0/3.0 chip.
3. Blue — the transistor that protects against reverse polarity at the power input.


Now for a closer look.
The step-down converter is built around an LM3150 PWM controller, two MOSFETs, and an inductor.


This PWM controller drives two transistors to implement synchronous rectification and improve efficiency. It also has a wide input voltage range (specified as 6 to 42 V) and can operate at frequencies up to 1 MHz.


The controller also has a very simple application circuit that uses few components, as well as a bootstrap supply that lets it use an N-channel high-side transistor. N-channel transistors generally have better characteristics than P-channel ones.
The converter chip's minimum output voltage is 0.6 V, but that applies to the chip itself, not this particular implementation.


Near the input terminal is the controller responsible for the Quick Charge modes. Its placement seems rather odd to me; it would make more sense near the output connector. That said, I haven't looked into the PCB routing, so the designers may have had their reasons.


This controller supports two modes, QC 2.0 and QC 3.0. For most users, the differences aren't critical:
QC 2.0 — switches the output voltage between 5/9/12/20 V
QC 3.0 — smoother adjustment across the 3.6–20 V range in 0.2 V steps.

QC 3.0 lets you adjust the source's output voltage more precisely, but fixed values of 5/9/12 V are usually enough. 20 V is used much less often.



The whole system works on a very simple principle: the controller receives information about what the power source should provide and, by intervening in the feedback loop, changes the output voltage as requested by the device.
The control commands are combinations of voltages on the USB data lines. The screenshot below shows the voltage levels and the corresponding supply voltage.
The table doesn't show the combination for requesting 20 V: 3.3 V on both lines. It also omits 0.6/3.3 V, which is used for QC 3.0 mode.
You can read more about it on Wikipedia.


A tiny blue LED is tucked away near the USB connector. It's connected to the USB port, and its brightness changes with the output voltage. I didn't test the USB connector, but it looks reasonably well made. Even so, I wouldn't recommend using it for high load currents.


Just in case, here's a more detailed photo of the individual components.


There are no components on the underside; this side of the board is partly used as a heatsink. There are tinned pads near the USB connector, which I used to connect the load. This is more reliable at high currents.


To check how the converter works, I used a USB tester with a Quick Charge protocol emulation function. By default, the output voltage is 5.24-5-25 V, which is within the standard's 4.75-5.25 V tolerance and helps compensate for the voltage drop in the load's power cable.


1. To check its capabilities, I used another tester with an auto-detection function. The list of supported modes is shown in the photo.
2. In QC 3.0 mode, the voltage adjustment step is 0.2 V.
3. The minimum setting is 3.86 V.
4. The maximum is almost 12.3
5. The elevated output voltage is the converter's own doing, since it overshoots by almost the same amount at every setting. In other words, set it to 5 V and you get 5.2 V at the output; set it to 9 V and you'll get about 9.2 V. I don't think that's very good, although it is within the tolerance range.
6. If you set it to 20 V, the output is still 12 V. That's a limitation of the Quick Charge controller used here.


My attempt to get anything above 5 V using my Lenovo P2 failed; the maximum was 5 V at 2 A. That's because the Lenovo uses MTK Pump Express, not Quick Charge.


For further experiments, I used an adjustable power supply, an electronic load, and a USB tester acting as a QC trigger to send commands for specific output voltages.


With no load, the converter draws 30 mA. Interestingly, the current doesn't depend on the input voltage, so at an input voltage of 36 V, the converter draws more than 1 W. In my opinion, the no-load power consumption is very high, so keep this in mind when powering it from batteries.


The remaining tests are hidden under the spoiler so as not to clutter up the review.


I compiled all the test results into one table, showing the output voltage and efficiency at different input voltages.
After entering the data, I noticed that:
1. With a 15 V input, the 12 V output sags noticeably, down to 10.74 V.
2. The output voltage rises slightly as the input voltage increases. With a 24–36 V input, it goes above 5.25 V.
3. Depending on the ratio of input to output voltage and the load current, efficiency reaches 94–94.3%, but there are also cases where it drops to 82.9%, clearly below the typical 93% stated in the specifications.



To sum up:
1. The converter works.
2. The build quality is pretty good.
3. Both QC 2.0 and QC 3.0 work properly.
4. It has input reverse-polarity protection.
5. The component selection is reasonably good.
6. Judging by the temperature rise, the maximum continuous current is 3.5–4 A at 5 V, 2–2.5 A at 9 V, and 1.7–1.8 A at 12 V. For short periods, the converter handles 5 A at 5 V, 3 A at 9 V, and 2.5 A at 12 V without issue.
7. Ripple is around 150–175 mV at a 5 V output and also with no load, which is a lot.

In short, I liked the converter more than I disliked it. It works reliably and caused no problems. It's usable, though with a few caveats.

That's all for now. As usual, I'm looking forward to your questions, and I hope you found this information useful.