For a consumer, one of technology’s greatest burdens is keeping your phone tethered to a charging cable while it charges. The iPhone 6, for example, takes over 2.5 hours to charge to full capacity—a mind-numbingly slow amount of time given today’s fast-paced environment.
Battery charge specs for popular phones on the market as of 2018. Image used courtesy of Forbes
In recent years companies have set out to fix this issue with the advent of fast-charging technologies. Big steps forward came when new generations of USB-C introduced faster universal charging capabilities. Still, the push continues as companies search for faster ways to charge devices.
Charging a Lithium-Ion Battery: The Basics
Before we can understand how fast-charging technologies work, we first must understand how a lithium-ion battery charges on a higher level. The standard lithium-ion battery charges to a cell voltage of 4.2 V. This charging occurs in two stages: constant current and constant voltage.
Stages in charging a lithium-Ion battery. Image used courtesy of Digi-Key
In the constant current phase, the charger supplies the battery with a constant current, increasing the cell voltage until the desired voltage is achieved. At this point, we enter the constant voltage stage. Here, the charger works to maintain a constant voltage on the cell in order to prevent overcharging.
Maintaining constant voltage causes the charge current to decrease over time until the battery reaches capacity, at which point charging is complete. This is also why charging the first 50% of a smartphone is significantly quicker than the last 50%.
For maximum efficiency in the charging process, a high-quality charging IC is required to ensure smooth transitions between stages.
Fast Charging from a Design Perspective
Fast-charging technologies utilize the same process but aim to deliver more power to the battery. Conventional USB chargers provide phones with .5 A at 5 V for a total of 2.5 W power delivery.
In a fast-charging device, the goal is to exploit the constant current phase, delivering as much current to the battery as possible. The caveat, according to Maker Pro’s tutorial on building mobile fast chargers, is that this must be done while still providing the same voltage so you don’t damage the battery.
To do this, designers generally supply larger voltages to the charger and then use a buck converter to step down the voltage to the desired value. In return (ignoring the converter’s efficiency), the current is stepped up proportionally.
For example, if .5 A at 20 V (10 W) was supplied, the converter would drop the voltage four times to 5 V. This would increase the current four times to 2 A. In this way, more power and current could be provided to the battery at the same voltage, allowing for four times faster charging than conventional charging.
Qualcomm’s Quick Charge 5
This week, Qualcomm announced the release of their Quick Charge 5.
The system benefits from a new generation of Qualcomm PMIC working in tandem with the SMB family of battery-charging ICs. Together, these devices provide Quick Charge 5 with some power-efficient specs.
Quick Charge 5 is comprised of battery-charging ICs and a new PMIC. Screenshot used courtesy of Qualcomm
Exploiting the constant current charging phase—the phase from 0–50% capacity—Quick Charge 5 claims to charge a 4500 mAh battery to 50% capacity in just 5 minutes. This is up to four times faster than the previous generation of Quick Charge.
Improved charging capability likely comes from an improved charging system, and this is exactly what we see in Quick Charge 5. Qualcomm says this system is able to provide 100W+ of power at over 70% greater efficiency than its previous generation.
Evolution of Qualcomm’s Quick Charge technology. Screenshot used courtesy of Qualcomm
Naturally, this has the added benefit of less heat, claiming to run up to 10 degrees celsius cooler than previous generations.
Faster Charge, Less Heat
Qualcomm claims the Quick Charge 5 is a game-changer in fast charging. Offering faster charging at greater efficiencies, and hence lower temperature will benefit the consumer and designer. The consumer no longer needs to wait hours for a charge, and the designer can be alleviated of thermal issues in their designs.
Already available on more than 1,200 mobile devices, this is a technology that may become a mainstay in the near future.