--- title: Charging Protocols and Fast Charging url: https://doc.liz6.com/en/hardware/08-power-and-protection/01-charging-protocols-and-fast-charging locale: en area: hardware tags: - hardware - power-and-protection date: 2026-06-30 modified: 2026-07-16 description: Charging Protocols and Fast Charging Charging Fundamentals The Essence of a Charger --- USB Power Delivery (PD) PD Versions | Version | Power | Voltage | Key Fe… --- # Charging Protocols and Fast Charging ## Charging Fundamentals ### The Essence of a Charger ``` Charger (Adapter) = AC-DC Power Supply + Protocol Chip Legacy Chargers: Fixed 5V output Fast Chargers: Dynamically adjust voltage/current based on device request Nominal Power ≠ Constant Output Power 65W Charger = "Capable of outputting up to 65W", actual power is determined by the device ``` --- ## USB Power Delivery (PD) ### PD Versions | Version | Power | Voltage | Key Features | |---------|-------|---------|--------------| | PD 2.0 | Up to 100W | 5/9/15/20V | Base protocol | | PD 3.0 | Up to 100W | +PPS | Programmable Voltage/Current | | PD 3.1 | Up to 240W | +28/36/48V (EPR) | High-power devices | ### PD Voltage Levels ``` SPR (Standard Power Range, ≤100W): 5V/3A = 15W 9V/3A = 27W 15V/3A = 45W 20V/5A = 100W EPR (Extended Power Range, >100W, PD 3.1): 28V/5A = 140W 36V/5A = 180W 48V/5A = 240W Note: Cables must also support the corresponding power! Standard Type-C cable = 3A (60W @20V) EPR cable = 5A (100W+), must have an E-Marker chip ``` ### PPS (Programmable Power Supply) — PD 3.0 ``` Traditional PD: Can only select fixed voltage steps (5V → 9V → 15V → 20V) Device steps down voltage internally → generates heat PPS: Device controls charger output in real-time Voltage: 3.3V~21V, 20mV steps Current: 0~5A, 50mA steps → Battery connected directly to charger output! → No internal step-down needed → No heat → Faster charging Galaxy S20+ Fast Charging = PPS Pixel Fast Charging = PPS Most Android Fast Charging = PPS ``` --- ## Proprietary Fast Charging Protocols ### Qualcomm Quick Charge (QC) ``` QC 2.0: 5/9/12/20V (negotiated via D+/D-) QC 3.0: 3.6~20V, 200mV steps (INOV) QC 4.0/4+: Compatible with USB PD, adds QC features on top of PD QC 5.0: 100W+, dual-cell series charging After QC 4.0+, it is essentially PD + QC enhancements Phones are also shifting towards PD/PPS; QC's influence is declining ``` ### Domestic Proprietary Protocols ``` OPPO/VOOC/SuperVOOC: Low voltage, high current (5V/6A~10V/6.5A) → Charger controls battery directly, phone stays cool → Requires dedicated cable and charger Huawei SuperCharge: Hybrid of VOOC + PD Early versions: 5V/4.5A or 4.5V/5A Later shifted towards PD/PPS Xiaomi Turbo Charge: PD/PPS + proprietary enhancements Current Status: Everyone is converging towards PD + PPS However, proprietary "ultra-fast charging" (>100W) remains non-standard ``` ### Proprietary Protocols vs. PD ``` Charging Speed (Actual): Proprietary 100W+ > PD 65W > PD 18W > 5V/2A Interoperability: PD chargers can charge most devices (15~100W) Proprietary charger + other brand phone = Slow charging (may be only 5V/2A) Recommendation: Buying a charger: Prioritize PD + PPS (better compatibility) Multiple devices: GaN multi-port PD charger (one charger for multiple uses) ``` --- ## Li-Ion Charging Curve ### CC/CV Charging Method (Foundation for all Li-ion batteries) ``` Stage 1: Trickle Charging When battery voltage < 3.0V, pre-charge with small current (~0.1C) Stage 2: Constant Current (CC) Charge at a set current (typically 0.5C~1C) Voltage gradually rises Stage 3: Constant Voltage (CV) Voltage reaches 4.2V (or 4.35V for high-voltage batteries) Current gradually decreases Current < 0.05C → Charging complete Voltage 4.2V ┤ ┌────────── │ ╱ │ ╱ │ ╱ 3.0V ┤─╱ └─────────────→ Time Trickle CC CV C-rate: 1C = Current equal to the battery's capacity value Example: 3000mAh battery, 1C = 3A charging current 0.5C = 1.5A ``` ### The Essence of Fast Charging ``` Traditional: Slow CC+CV throughout → Safe but slow Fast Charging: Large current CC at low battery levels → Gradually slows down after ~50% "0-50% in 15 minutes" is possible "0-100% in 15 minutes" is impossible (CV stage is unavoidable) Fast charging accelerates the CC stage CV stage cannot be accelerated (due to battery safety requirements) ``` --- ## BMS (Battery Management System) ### Basic Functions ``` Protection: - Overcharge protection (each cell > 4.25V → disconnect) - Over-discharge protection (each cell < 2.7~3.0V → disconnect) - Overcurrent/short-circuit protection - Temperature protection (0~45°C charging, -20~60°C discharging) Balancing (Multi-cell): - Passive balancing: Discharge high-voltage cells via resistors - Active balancing: Transfer energy from high-voltage cells to low-voltage cells Metering (Gauge): - Coulomb Counter: Integrate current → Accurate SOC - Voltage lookup table: Rough, not accurate enough ``` ### Multi-cell Batteries ``` Single-cell Li-Ion: 3.7V nominal, 4.2V full 1S = 3.7V, suitable for low-power devices Two-cell series (2S): 7.4V nominal, 8.4V full Common in: Walkie-talkies, RC models, handheld devices Three-cell series (3S): 11.1V nominal Four-cell series (4S): 14.8V nominal Common in: Laptop batteries, power tools Multi-cell batteries must have balancing charging! Otherwise, one cell may overcharge → catch fire/explosion ``` --- ## Wireless Charging ### Qi (Inductive) ``` Based on electromagnetic induction (two coils) Frequency: 110~205 kHz Power: BPP (Base): 5W EPP (Extended): 15W MPP (Qi2/Magnetic): 15W (Apple MagSafe protocol) Qi2: Open standard based on Apple MagSafe Efficiency: Typically 70~80% Alignment: Coils must be aligned → Qi2 adds magnets (MagSafe mode) ``` ### Other Wireless Charging ``` Apple MagSafe: 15W (Qi2 compatible), magnetic alignment Samsung Fast Wireless: 15W (proprietary extension) Xiaomi/OPPO Proprietary: Up to 50~100W (but generates significant heat) AirFuel (Resonant): Longer distance, simultaneous charging for multiple devices, but not widely adopted ``` --- ## Fast Charging Power Selection Reference ``` Device Typical Fast Charging Power ────────────────────────────────────── TWS Earbud Case 5W (No fast charging needed) Smartwatch 5~10W Smartphone 18~65W (Mainly PD/PPS) Tablet 20~45W Ultrabook 45~65W PD All-around Laptop 65~100W PD Gaming Laptop 100~240W PD 3.1 or proprietary charger Small IoT 5W (Micro USB or Type-C 5V) ``` --- *Keywords: USB PD, PPS, QC, CC/CV, BMS, C-rate, Balancing Charging, Qi, Wireless Charging*