As the performance of mobile phones, computers, and other technological devices become more and more powerful, the power consumption also increases gradually, how to charge faster has become a topic of concern to users. However, in the actual experience of users, the following problems have been bothering users:
  1. The phone has a fast-charging function, but why is the charging speed still slow?
  2. Is there a security risk with fast charging? Full of panic about charging explosions?
  3. Uneasy due to the heat of the phone when charging while playing
There are many fast charging technologies on the market. Which one is right for your phone? Below, will explain two mainstream fast charging technologies, Quick Charge fast charging (QC) and USB Power Delivery fast charging (USB-PD).

What's Fast Charging

Fast charging, is a comparative concept of charging speed in a unit of time. For example, to charge the same mobile device, within the maximum allowable load range, use a high-power charger to increase its charging speed and save charging time. It originally took three hours to fully charge, but it only took one hour, this is what means "fast charging".

The Principle of Fast Charging

According to electrical knowledge, voltage (volts, V) times current (amps, A) can get power (watts, W). For the same device, the higher the charging power, the shorter the charging time. At present, fast charging technology can be achieved in the following three ways:

  1. High Voltage Low Current Mode: Increase charging power by boosting voltage
  2. Low Voltage High Current Mode: Increase charging power by increasing current
  3. High Voltage High Current Mode: Boost voltage and boost current at the same time

To be short, fast charging is to effectively improve the charging speed of the device and shorten the charging time within a safe load range. At present, the mainstream fast charging technologies on the market include Quick Charge™ (QC) developed by Qualcomm and USB Power Delivery (PD) defined by the USB-IF.

Difference Between Quick Charge & PD Fast Charge

What's Quck Charge

QC is the abbreviation of Quick Charge technology of Qualcomm. Since Qualcomm's Snapdragon mobile platform is currently the most popular in smartphones, Quick Charge is the most popular fast charging technology in the market. In addition, there are also many non-Snapdragon mobile phones that support Quick Charge, such as Samsung S8, S9, Note 8, etc.

Quick Charge technology first adopted the "low voltage and high current" mode, which enhances the charging power by increasing the current to 2A (usually 0.5A for charging), which was the upper limit of the current that the Micro USB connector can withstand. Then Qualcomm turned to the development of "high voltage constant Current" mode, which increases the charging power by boosting the voltage. Until the Type C connector gradually matures and the upper limit of the current it can withstand increases, the "high voltage and high current" mode becomes feasible from theory.

At present, Qualcomm has launched the latest fast charging version QC 5.0, which is the world's first fast charging technology that can support more than 100w charging power. At the same time, it is truly compatible with USB-PD charging standards and features.

Historic Version of QC Fast Charging

What's PD

PD fast charging is the abbreviation of USB Power Delivery, which is a power transmission specification defined by the USB-IF Association. At present, PD fast charging can be divided into five profiles: 10W, 18W, 36W, 60W, and 100W. The voltage is 5V, 9V, 12V, 20V, can be used with Type C connectors that support up to 5A.

What should be noted is that although PD fast charging can support up to 100W of power theoretically, the actual charging power supported by the mobile phone depends on the announcement of the manufacturer.

In addition, in order to unify the standard, chargers that support USB PD fast charging must use the Type-C interface, which can also be used in tablets, laptops, TVs, and other products, and is compatible with Qualcomm's latest QC 5 and QC 4 fast-charging technologies.

historic version of PD fast charging

Does fast charging reduce battery life?

Many users worry that fast charging will damage the battery life. In fact, as charging technology matures, current fast charging technology can strike a good balance between the convenience of fast charging and the impact on battery life.

The maximum charging power supported by the mobile phone does not mean that the charging is performed at the highest power during the whole charging process, but will be segmented according to the current power of the mobile phone. If the highest power is used in the early stage, the power will be gradually reduced in the middle stage, until the slow "trickle charging" is performed at the end.

Some chargers have a built-in charging IC, which can effectively reduce the heat generated by the mobile phone during fast charging and reduce the damage to the battery. At the same time, these IC chips can also limit the charging power of mobile phones that do not meet the same fast charging protocol.

There are also built-in temperature control components in some chargers. When an abnormal temperature increase is detected, the fuse inside the charger will melt, isolating the current input physically.
Of course, there are indeed some inferior charging accessories on the market. These charging accessories may be very cheap, but there may be hidden dangers such as leakage and spontaneous combustion. Be cautious when purchasing.

Charging cable is also important

Many consumers choose mobile phones and charging heads that support fast charging, but still use charging cables that only support 2A or less current for charging, resulting in the inability to meet fast charging specifications higher than 2A. For example, if the mobile phone supports 27W fast charging, It is achieved by the output combination of 9V / 3A, but since the charging cable only has a maximum current of 2A, the charger can only charge the mobile phone with a power of 18W of 9V / 2A.


This information is provided for ease of reference only. This information is not and should not be considered an official communication of the USB Implementers Forum (USB-IF) & Qualcomm. Official information about the USB-IF is available on its website at, or directly from the USB-IF. Official information about Qualcomm is available on its website at