Modern devices use sophisticated protocols to negotiate power delivery, enabling fast charging and optimal power management.
USB Power Delivery (USB-PD)
Definition: A universal fast-charging standard that can deliver up to 240W over USB-C.
Power Profiles
| Profile | Voltage | Max Current | Max Power |
|---|---|---|---|
| Profile 1 | 5V | 3A | 15W |
| Profile 2 | 9V | 3A | 27W |
| Profile 3 | 15V | 3A | 45W |
| Profile 4 | 20V | 5A | 100W |
| Extended (PD 3.1) | 28V, 36V, 48V | 5A | Up to 240W |
Voltage Negotiation Process
sequenceDiagram
participant Device
participant Charger
Device->>Charger: Connect
Charger->>Device: Default 5V @ 0.5A
Device->>Charger: Request Capabilities
Charger->>Device: Send Power Profiles
Note over Charger: 5V/3A, 9V/3A, 15V/3A, 20V/5A
Device->>Charger: Select Profile (e.g., 20V @ 3A)
Charger->>Device: Accept & Switch Voltage
Note over Device,Charger: Charging at 60W
Device->>Charger: Request Lower Power (battery full)
Charger->>Device: Adjust to 5V @ 1A
Real-World Charging Example
1. Laptop connects to 100W USB-C charger
2. Charger sends: "I support 5V/3A, 9V/3A, 15V/3A, 20V/5A"
3. Laptop analyzes battery state (50% charged, can accept 65W)
4. Laptop requests: "Please provide 20V @ 3.25A (65W)"
5. Charger validates: Cable rated for 5A ✓, Can provide 65W ✓
6. Charger responds: "Accepted, switching to 20V"
7. Charger delivers 20V @ 3.25A
8. As battery reaches 80%, laptop requests lower power
9. Laptop requests: "Please provide 20V @ 2A (40W)"
10. Charger adjusts to 20V @ 2AQualcomm Quick Charge
Definition: A proprietary fast-charging technology that adjusts voltage and current for optimal charging speed.
Quick Charge Versions
| Version | Max Power | Voltage Range | Key Feature |
|---|---|---|---|
| QC 1.0 | 10W | 5V @ 2A | Basic fast charging |
| QC 2.0 | 18W | 5V, 9V, 12V | Multiple voltage levels |
| QC 3.0 | 18W | 3.6V - 20V (200mV steps) | Fine voltage control (INOV) |
| QC 4.0 | 27W+ | USB-PD compatible | PD integration, cooler charging |
| QC 5.0 | 100W+ | USB-PD 3.0 PPS | 10°C cooler, 70% efficient |
How Quick Charge Works
graph TD
Start([Device Connected]) --> Handshake[Handshake via D+ D- lines]
Handshake --> Detect{QC Compatible?}
Detect -->|No| Standard[Standard 5V charging]
Detect -->|Yes| Request[Device requests voltage]
Request --> Adjust[Charger adjusts voltage]
Adjust --> Monitor[Monitor temperature & current]
Monitor --> Check{Battery > 80%?}
Check -->|No| Monitor
Check -->|Yes| Reduce[Reduce to trickle charge]
Reduce --> End([Charging Complete])
Standard --> End
Safety Mechanisms
- Over-Voltage Protection (OVP): Prevents voltage spikes
- Over-Current Protection (OCP): Limits maximum current
- Over-Temperature Protection (OTP): Reduces power if too hot
- Short-Circuit Protection: Shuts down on short circuit
- Cable Detection: Verifies cable can handle requested power
Temperature Management
Temperature Thresholds:
- Normal: < 40°C → Full speed charging
- Warm: 40-45°C → Reduce to 80% power
- Hot: 45-50°C → Reduce to 50% power
- Critical: > 50°C → Stop fast charging, use 5V onlyOther Fast Charging Protocols
| Protocol | Manufacturer | Max Power | Special Feature |
|---|---|---|---|
| SuperVOOC | OPPO | 240W | Dual-cell charging |
| Warp Charge | OnePlus | 65W | Low-voltage, high-current |
| Adaptive Fast Charging | Samsung | 45W | PD compatible |
| TurboPower | Motorola | 68W | QC compatible |
Comparison: USB-PD vs Quick Charge
| Aspect | USB-PD | Quick Charge |
|---|---|---|
| Standard | Open (USB-IF) | Proprietary (Qualcomm) |
| Max Power | 240W | 100W+ (QC 5.0) |
| Connector | USB-C required | USB-A or USB-C |
| Compatibility | Universal | Qualcomm chipsets (QC 4.0+ supports PD) |