This article explains the principles behind fast charging, compares different fast charging technologies, and discusses why different brands' fast charging solutions aren't always compatible.
The Basics of PD Fast Charging
What is PD Fast Charging?
PD fast charging stands for USB Power Delivery. It's a widely used fast charging standard for delivering power via USB. Most PD fast charging solutions today use Type-C ports.
How PD Fast Charging Works
The USB-C port has multiple pins, but only 8 are used for transmitting electricity: 4 for Ground (GND) and 4 for Voltage Bus (VBUS). These effectively act as two wires for charging.
However, directly increasing the voltage or current can be problematic. Traditional USB devices often only accept 5V, while some chargers can output up to 20V. To address this, the USB-IF (Implementers Forum) added a CC (Configuration Channel) pin to the USB-C port.
The Role of the CC Cable
The CC cable enables communication between the charger and the device. When connected, the charger sends a Power Data Object (PDO) to the phone, listing its power capabilities. The phone then selects an appropriate voltage and current, like 9V and 3A. The charger only provides the requested power. A 240W PD charger will only output 27W to a 27W phone, preventing damage. This communication process takes milliseconds. PD fast charging also requires the CC cable in addition to the power cable.
PD Fast Charging Cables
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Apple's PD fast charging cable includes a CC cable and a D+ D- cable (USB 2.0 data cable), allowing for low-speed data transfer.
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Xiaomi's fast charging cable has fewer cables but achieves the same effect due to symmetrical design. Both cables can be used interchangeably for PD fast charging.
Currently, PD fast charging can support up to 240W.
Why Domestic Brands Use Proprietary Fast Charging
Limitations of PD Fast Charging for Mobile Phones
PD fast charging often uses high voltage and low current. While suitable for laptops, mobile phone batteries typically operate at lower voltages (3.7V-4.5V). Using a higher voltage requires voltage conversion, which wastes energy and generates heat. The small size of mobile phones makes managing heat challenging.
The Advantages of Low-Voltage, High-Current Solutions
Mobile phones benefit more from low-voltage, high-current charging. Domestic brands have developed proprietary fast charging protocols based on this principle.
Example: VOOC Charging
In 2014, Oppo's VOOC technology increased charging speed from 5W-10W to 20W by completing voltage conversion in the charger. This prevented the phone from converting the voltage twice, reducing energy loss and heat. The charger handles most of the heat.
With reduced heat in the phone, higher currents can be used, increasing charging power. Thicker copper wires in the Type-C cable support currents of 4A or higher without overheating.
Key Features of Domestic Fast Charging Solutions
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Low-voltage, high-current design
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Double capacitors for handling higher currents
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Accelerated charging lines
The main difference between these protocols is their non-public communication methods.
Compatibility Issues
Using a mismatched charging cable may result in slow charging. Super fast charging cables contain chips that verify the charger before allowing high current output, preventing fires caused by faulty cables.
The Evolution of PD Fast Charging
While Apple still primarily uses basic PD fast charging, domestic brands have customized their hardware for optimal performance with their proprietary protocols.
PD 3.0 and PPS
The release of PD 3.0 introduced Programmable Power Supply (PPS), which allows for more precise voltage adjustments (20mV increments between 3.3V and 21V) and supports currents up to 5A.
PPS allows for direct charging at voltages like 4.5V, reducing the need for voltage conversion in the phone and minimizing heat.
The Future of Fast Charging
While early PD protocols weren't ideal for mobile phones, improvements like PPS have led to increased adoption. However, proprietary protocols remain popular due to their higher power capabilities and better optimization.