New phone models must have a fast charging
feature. And thanks to this function, we can quickly charge the phone's battery
even in the middle of our busy schedule. However, this fast charging has been
developed according to different standards by different companies. There are
some fast chargers that only work with certain charging cables and chargers,
while other fast charging features use much higher voltages. And you might be a
bit confused about these things, so we came up with this tune to clear that
confusion.
In short, fast charging increases the current
supplied to the battery to charge it faster. And the basic USB specification
only delivers 0.5 amps (A) from 2.5 watts (W) of current to 5 volts (V).
However, the fast charging technology increases the basic charge. Huawei 10V/4A
SuperCharge can charge at 40W, and Samsung's latest Adaptive Fast Charging can
charge at 15W. And the fast charging technology developed by some Chinese
companies is capable of fast charging at 100W. All fast charging functions
ultimately have as a result, one goal, namely to charge the battery more in a
very short time.
I discussed the basics of fast charging
above. But how to quickly charge the battery is more complicated. Before we
know that, let's look at the differences between the various fast charging
standards.
Details on fast charging standards
USB power supply
USB Power Delivery (USB-PD) is a fast
charging specification that has been continuously published since 2012 by
USB-IF. And this standard can be used in the USB port of any device, but it
must contain the circuit and software required by its manufacturer. Like other
fast charging standards, USB-PD uses a data protocol to communicate between the
charger and the phone. And with this, it is determined how much the device will
have a tolerable phase.
USB Power Delivery boosts basic USB charging
up to 100W. It also splits the total power into different ratings that operate
at different voltages. And the 7.5W+ and 15W+ power modes are suitable for phones,
while the 27W and higher power modes are suitable for laptops and other power
devices. These standards also support two-way power systems, with which you can
charge any other device with your phone.
Google's Pixel line of phones uses the
official Power Delivery specification, and many flagship smartphones currently
support the technology. Apple also uses this standard in its phones such as the
iPhone 8, iPhone X, iPhone XS and the latest MacBooks. However, many companies
prefer to use their own proprietary fast charging technology.
Qualcomm Fast Charging
Qualcomm's proprietary fast charging
technology has been the default standard in the smartphone industry since it
was popular for fast charging before USB Power Delivery. In its latest version
of fast charging 4.0+, the speed and range of supported devices have also
increased significantly.
Fast charging is an optional feature of the
Qualcomm Snapdragon processor. However, just because a phone has a Qualcomm
processor doesn't mean fast charging is supported. However, many phones like
the LG V40, Xiaomi Mi 9, Samsung Galaxy Note 9, HTC U12 Plus and many others
support fast charging. In addition, due to the different standards of different
brands, this chipset supports older chargers and third-party fast chargers.
Other standards
In the smartphone ecosystem, thousands of
phone models use proprietary fast charging technology. However, some of these
standards are proprietary to some companies. In addition, other companies
repackage Power Delivery or Quick Charge under different brands or with some
modifications – for example, Samsung's Adaptive Charging and Motorola's Turbo
Charging are notable among them.
Oppo VOOC and Huawei SuperCharge developed
fast charging technology slightly differently. This fast charging greatly
increases the current for charging at high power rather than increasing the
applied voltage. These SuperCharge, Super VOCC and WarpCharge from OnePlus have
increased their fast charging capacity over the years, resulting in one of the
fastest fast charging on the market.
The device may support multiple fast charging
standards or at least be capable of fast charging through different fast
charging methods. However, if you use different chargers or different charging
cables, you may not reach the default fast charging speed when charging your
phone.
Because we tested the fast charging
technology on several phones, the speed at which your phone will charge depends
on the charger and charging cable. However, we got the best results using the
charger and charging cable that came with the phone.
How fast charging a lithium-ion battery works
We have discussed various fast charging
standards above, now let's see how fast charging increases battery charging
speed. Lithium-ion batteries used inside any smartphone and other electronic
devices do not typically charge in a linear fashion. Because the battery is
charged by splitting the charge cycle into two separate parts.
The first stage increases the voltage or
current step. Normally, the battery voltage is stable below 2V, which can be
boosted up to about 4.2V by fast charging. And basically it varies depending on
the battery. At this stage, the battery reaches a peak current that remains
constant until the battery voltage reaches its peak.
After that, the voltage remains unchanged and
the peak current starts to decrease. Batteries that charge with constant
current charge at a slow rate. But that's exactly why the first 50 to 60
percent of the phone's charge is very fast, but it takes a long time to fully
charge.
Fast charging technologies use a constant
current phase. K continues to draw as much current as possible until the
battery reaches its maximum voltage. So fast charging technologies are most
effective when your phone's battery is 50 percent charged, but once it's 80
percent charged, fast charging has no effect, meaning it starts charging
normally again. By the way, the constant current charging point is a charging
point suitable for long-term use of the battery. On the other hand, a higher
constant voltage is detrimental to battery life.
Finally, the amount of voltage and current
flowing through the battery is controlled by a charge controller circuit inside
the phone. Temperature and voltage sensors are connected to this circuit, and through
this controller circuit, the battery charging speed and battery life cycle are
optimized so that the battery can be used for a long time.
High voltage fast charging?
You may be wondering if fast charging at high
voltage is bad for your battery. To be clear, if the lithium ion battery is 3
to 4.2V, is it dangerous to charge the battery with a high voltage charger?
Normally this is dangerous, but in
smartphones the charging circuit lowers the charger voltage and increases the
current. This means that this charging circuit keeps the power transferred to
your phone (P = IV) the same, but shifts the voltage to the correct value.
However, fast charging cables cannot convert to AC voltage. If you look at the
back of the charger, you will see a dashed DC icon (⎓). And remember that the USB cable is a DC
power system, not an AC power system.
High voltage fast charging circuits use a
step-down switching power supply, also known as a buck inverter. This circuit
takes a high DC voltage and converts it to a low DC voltage. In general, it
draws a charge by multiplying the current supply current by its opposite amount
of current. It also includes switching the input voltage to charge the
capacitor with a large current.
After the 10V / 1A to 5V converter, it
typically receives a current of 2A. And in the real world, these converters
always have some loss involved (they're usually 90 percent efficient).
Additionally, switching power supplies generally dissipate less power than
linear regulators.
Why use high voltage?
There are two main reasons for using high
voltage. First, a switching power supply is more efficient than a linear
regulator, reducing the voltage by reducing the heat dissipation of your phone.
And because of that, it plays a very important role in keeping our phone and
its battery cool.
The second reason is that USB cables,
especially long ones, waste a lot of power. A resistor, such as a length of
cable, will cause current passing through it to cause a voltage drop (Ohm's law
V=IR). At high voltage and low current, there is comparatively less power loss
for the same cable length. And so it's more efficient, and the mains is
hundreds of volts, not the 5V of your charger.
However, the main difference is that a buck
converter is more energy efficient than a linear regulator. In addition, the
maximum output power and switching frequency of a transistor depends on its
size of inductor, capacitor and voltage ripple. And because of this, it is
possible to get much more current than a normal linear voltage regulator. And
that's why the low-voltage 5V fast charging technology from Huawei and OPPO can
charge batteries faster than the high-voltage money-switching versions from
Qualcomm and Samsung.
The diagram above shows how MediaTek's
PumpExpress 3.0 and 4.0 can increase the charging current up to 5A. When
charging the battery via a 5A charging cable, this technology is able to bypass
the current at a higher voltage. In this case, the circuit will lower the
charging voltage Vbus for maximum efficiency.
The last word
There are different fast charging standards,
each with their own advantages and disadvantages. That's why there are so many
fast charging standards on the market, as each company prefers its own method
of increasing charging speed and extending battery life.
A few generations ago, high-voltage charging
became the norm, and now technologies use low controlled voltage and high
current to increase speed.
USB Power Delivery has already become very
popular. This will likely serve as the backbone of USB charging standards
moving forward, so I expect fast charging to improve further in the near
future.
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