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Knowledge about 15W wireless charging

1. The concept of 15W wireless charging

15W wireless charging is backward compatible with 10W, 7.5W, and 5W.

At present, most 10W wireless chargers on the market can do 15W, and they all use one chip, but the problem is that the product heats up. Because only adding the EPP protocol to the 10W wireless charging is a software workload. Only a few early 10W wireless charging solutions can't do 15W.

The point is, the 15W wireless chargers on the market are only for test racks and use the EPP protocol. The charging of mobile phones cannot reach 15W, because the 15W of Apple, Huawei, and Samsung all add private agreements on the basis of EPP.

Similarly, some people want to do 20W, 30W, 40W, 50W wireless charging. The first thing to solve is what kind of product you want to charge, otherwise it is just a mirror in the water.

Then comes another important question, the power issue:

When we were choosing the 15W wireless charging solution, we found that the same 15W test rack was used. As a result, the heat of plan A was serious, and the heat of plan B was not serious. Is it possible to quickly determine that the efficiency of plan A is not as good as that of plan B?

If you judge in this way, you may miss a good solution, the reason is that the 15W we see on the test frame is sometimes not the real full power 15W

Maybe the B scheme only reaches 13W, and it also shows 15W, and the other A scheme with 15W only shows 15W. It is natural that the A scheme has serious heat, but the A scheme has more power.

How to judge it? One only requires junior high school physics knowledge + logical analysis ability + a lot of time test comparison. There is also an unconditional trust in a professional wireless charging solution provider and hand it over to them.



2. Understand the power supply of 15W wireless charging

The power supply of 15W wireless charging is generally required to be 9V or 12V. There is no requirement that it must be 9V or 12V. Different solutions are different. This way of power supply 1: Directly supply 9V or 12V; 2: Deceive 9V, 12V through QC or PD

All 15W wireless chargers on the market support QC, otherwise it would not be called 15W. From the circuit point of view, at least D+ and D- should be connected to the chip (support QC); either CC1 or CC2 should be connected to the chip (support PD)

However, it should be noted that not all 15W wireless charging solutions can directly supply 9V or 12V, so if you want products such as desk lamps and speakers to require direct power supply, you must know whether the selected solution supports direct supply.

In addition, you must know that 10W-15W wireless charging does not have 5V2A, 5V3A, and 5V power supply 15W wireless charging can only output 5W. This is a standard issue, just abide by it. It is not recommended to challenge the standard unless you are Apple or Huawei.


3. Whether it supports NTC protection, overcurrent protection, FOD, whether the indicator light is adjustable, etc.

All 15W wireless chargers on the market support these functions, so there is no need to ask them. The question to ask is how far you want to go with these features, such as:

Most of the NTC temperature protection software does protection at 65 degrees and resumes work at 45-50 degrees. That some solution company software can reduce the power as the temperature rises, and some can't.


The 15W overcurrent protection is generally around 2.3A, but some customers limit the power in order not to seriously reduce the current limit for the product to heat up, but what is seen on the test stand is a virtual 15W.

FOD can generally be achieved, but everyone generally uses the inner ring of the tangent coil of a dollar coin to test. If your shell is thick and you need 5MM to measure the FOD, then you must propose it to your solution provider in advance, not All programs can be satisfied.

The indicator light can generally be changed, but not all wireless charging lights can meet the requirements, because most of the wireless charging MCU memory is used to the extreme, so the main thing to do a good breathing light is to have enough space.

In addition, some chips are OTP, and the solution provider who sells it is not willing to change the way of the light when considering stocking.


4. Whether to pass QI, temperature requirements, and peripheral complexity requirements

After QI, it is generally divided into BPP (referring to 5W) and EPP (referring to EPP). The cost of the QI solution is much more expensive, nearly double.

For temperature requirements, generally the extreme low-cost solution must have high temperature, but it is not necessarily high in absolute temperature; the solution with MCU with full bridge and SOC solution has moderate temperature; the solution with real low temperature must be hardware-driven MOS and external MOS , but the disadvantage of this type of scheme is that the periphery is more complicated. (As shown in the figure, a triode is added as a hardware driver), and the cost is lower than that of the MCU with full bridge and SOC solution.


5. Requirements for 15W magnetic wireless charging

In fact, 15W wireless chargers on the market can be used as magnetic suction

But adding a magnet will affect the charging distance, efficiency, and FOD sensitivity.

This needs to be verified in combination with the actual product, such as the selected magnet, coil, shell thickness, requirements for charging time, and requirements for FOD. These factors will affect each other. If you use a magnetic wireless charger with high FOD requirements, you may sacrifice the charging efficiency of charging Huawei, Xiaomi, and Samsung mobile phones, resulting in serious heating of these mobile phones. Because Apple mobile phones are designed for magnetic attraction, and other mobile phones do not consider the problem of magnets.


6. 15W wireless charging coil and resonant capacitor

Most of the 15W wireless charging coils on the market use the same A11 coil as the 5W and 10W coils (6.3uH, internal resistance 50-60m ohms, Q value above 70); resonant capacitors are generally 4 1206 104 or one 404 CBB

But the coil that has passed EPP certification needs to choose MP-A2 (10uH, internal resistance 50-60m ohm, Q value above 70), with 254 CBB

But you must know that the magnetic wireless charging cannot pass the QI certification. QI stipulates that the 70mM of the coil cannot have a magnet. But the WPC is said to be considering changing the rules for magnetic attraction.


7. Whether to pass CE or KC

It is relatively easy to wirelessly charge CE, and it can be basically passed.

But KC is relatively strict, which depends on the LAYOUT level of the engineer. We have a special article explaining wireless charging LAYOUT. But in fact, this is still a solid basic skill of electronic knowledge. With a good foundation, LAYOUT can use any board for 2-3 years, not limited to wireless charging, because LAYOUT's things are not unique to wireless charging, and are basically universal; if the basic skills are not solid, both Even after more than 10 years, I may not be able to draw a good board, and I can only limit myself to experience and relying on God to eat. It's hard to LAYOUT with just one article. It can only be said that it has improved or accumulated knowledge.

Post time: May-21-2022