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QQC Q-Swap Power Bank Tear-Down

Q-Boost Open Frame

Now here’s a somewhat puzzling first look at the Q-Boost frame’s internals. From the exterior shape, you may have expected the electronics to be tucked away in the connector and contact pad areas. But this picture shows the space immediately next to the type-A socket to be empty. If you pay close attention to the type-A connector and follow the PCB edge, you can see it extend into the side wall all the way to the cell retention clip.

Locating electronics into hollow walls is one way of saving space.


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Q-Boost Cell Retention

Whereas a budget-oriented manufacturer would likely have molded the retention tabs directly into the frame and relied on the frame’s flex to hold the cell in, QQC went with separate plastic tabs powered by tiny springs on each side. To top that off, a metal insert in the frame prevents the spring from eventually wearing its way through the outer wall it rests against.

As far as plastic housings go, no expense was spared here.


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Q-Boost Innards

The attention to detail continues with a mechanical support frame around the type-A connector to help lock it in place, a rubber strip on a piece of phenolic cardboard to provide pressure for the cell contacts, and a thin rubber strip to hold things in place for assembly. As an interesting design twist, the Q-Boost’s circuit board is so thin that QQC could afford to build the whole thing as a single piece, then bend the board’s contact area into place to eliminate wiring between boards.

While chips on flat flex cable (FFC) are commonplace, I believe this is my first time seeing a manufacturer flex a regular (albeit thin) circuit board.


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Flattened Q-Boost

I gingerly straightened the Q-Boost’s board to have a flat look at it, as if freshly cut off from the manufacturing panel. Shockingly enough, there is next to nothing on it. We have a one-microhenry inductor next to a QFN-style 6939, which must be a boost converter with integrated drivers, an SOT25 93F04 also found in the Q-Cell, which may be a linear voltage regulator, an SOT343 ML23 that I suspect is a One-Wire device based on how the Q-Cell’s D_P signal gets routed straight to its immediate neighborhood, and a SOT26 FT4KPK that connects to the type-A port’s data lines, likely making it a charging mode detection chip. I could not find definitive matches for any of these.

I was expecting some form of processor to talk with the Q-Cell’s micro-controller.


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Q-Boost SMD Soldering

Soldering uniformity looks a lot better in the Q-Boost than the Q-Cell, with no excess solder balling up on the pads or component leads. Solder balling around the 6939 is more subtle than it was on the Q-Cell’s QFN, and the 0603/0402 components have the characteristic uniform concave filleting with full pad coverage. Did QQC use a thinner solder paste stencil for this board?


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Q-Boost Through-Hole Soldering

While the SMD-side soldering looked very good, the type-A connector’s soldering is slightly worse. Although the joints themselves look fine, there is leftover solder flux on the board that lint gets stuck to. And embedded in that solidified flux are a few tiny solder globules like the one circled in red, along with a smaller one further to its right. These could become a short-circuit hazard if they ever broke loose from the flux.

I doubt the Q-Frame will ever get hot enough to liquefy the flux and free the globules, but I would have preferred that they both went away in the ultrasonic cleaner.


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Missed Opportunity

I mentioned earlier that the combination of taper and different corner radii on the Q-Cell made it impossible to insert the cell incorrectly. I found one practical disadvantage to this: if you could insert the Q-Cell rotated 180° so its contacts faced away from the Q-Frame contacts, then you could use the Q-Frame as a Q-Cell contact cover, greatly reducing the risk of shorting the exposed Q-Cell contacts and eliminating the live Q-Frame type-A port when not in use.


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Q-Cell Charging Circuit

Remember how I said I’d expect the charging regulator to operate somewhere north of 1 MHz? Here I am measuring the regulator’s output ripples and there are effectively none to speak of. All we see are the chip’s very fast switching transients, which demonstrate irregular intervals as short as 300ns and as long as 1µs. There may be a feedback loop stability issue going on.

This sort of artifact is no good for efficiency due to increased transistor switching and inductor losses. That might explain the unbearably hot inductors.


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Q-Cell Output Liveliness Test

One question I brought up earlier was whether or not getting power out of the Q-Cell might be as simple as hooking it up. For safety reasons, I expected output current to be extremely limited (say, 10mA) until some sort of handshake was completed.

In order to determine which one was correct, I connected a 20W halogen bulb across the battery terminals and the bulb lit up to a dim orange glow, drawing 930mA in the process.

There's no secret handshake here; just remain below the over-current cut-off.


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Q-Cell Short-Circuit Behavior

How high does the Q-Cell’s short-circuit current go, and how quickly does it disconnect its output when such a short happens? To find out, I shorted the pack’s contacts with a 0.1Ω resistor and recorded the cell’s response with an oscilloscope. Since I = V / R and R = 0.1, the current is the same as the voltage multiplied by ten. Here, we see the Q-Cell putting out roughly 22.5A for 9.5ms before cutting off its output.

At first, I thought the not-quite-vertical rise meant that the Q-Cell had some sort of current rise rate limit. Then I realized that it may simply be my ceramic wire-wound resistor acting as an inductor.

Let’s see what happens with a beefier resistor.


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Daniel Sauvageau is a Contributing Writer for Tom's Hardware US. He’s known for his feature tear-downs of components and peripherals.