Power Rating Calculator
Understanding Power Ratings
How to Calculate Power Rating of Resistor?
To calculate resistor power rating:
- Using current: P = I² × R
- Using voltage: P = V² / R
- Using both: P = V × I
- Add 100% safety margin
SMD Resistor Power Rating Chart
| Package Size | Power Rating | Max Voltage |
|---|---|---|
| 0201 Resistor | 1/20W (0.05W) | 25V |
| 0402 Resistor | 1/16W (0.063W) | 50V |
| 0603 Resistor | 1/10W (0.1W) | 75V |
| 0805 Resistor | 1/8W (0.125W) | 150V |
Peak Power Rating Considerations
Important factors for resistor peak power rating:
- Pulse duration tolerance
- Maximum peak voltage capability
- Thermal time constant
- Repetition rate effects
- Ambient temperature impact
Surface Mount Technology
Key aspects of SMD resistor power rating:
- PCB thermal design considerations
- Pad layout optimization
- Thermal vias implementation
- Copper plane connection
- Component spacing requirements
Through-Hole Resistor Power Rating Chart
| Type | Power Rating | Max Voltage | Physical Size |
|---|---|---|---|
| Carbon Film | 1/4W | 250V | 6.3 × 2.4mm |
| Metal Film | 1/2W | 350V | 9.2 × 3.2mm |
| Wire Wound | 1W | 500V | 12.7 × 4.2mm |
| Ceramic | 2W | 750V | 15.7 × 5.2mm |
| Metal Oxide | 3W | 1000V | 18.5 × 6.4mm |
| Power Wire | 5W | 1500V | 24.0 × 8.0mm |
Thermal Design Considerations
Key thermal design factors for power resistors:
- Heat sink requirements and thermal interface materials
- Airflow and ventilation planning
- PCB copper area and thermal vias design
- Component spacing and thermal isolation
- Maximum operating temperature limits
- Thermal resistance path optimization
- Environmental temperature effects
Common Applications
Power resistors are commonly used in:
- Power supplies and voltage regulators
- Motor control and braking circuits
- LED current limiting
- Heaters and heating elements
- Load testing and power distribution
- Current sensing and measurement
- Snubber circuits and surge protection
Troubleshooting Guide
Common power resistor issues and solutions:
Resistor overheating
Check power rating, improve cooling, or use higher rated component
Voltage breakdown
Verify voltage rating and peak voltage exposure
Thermal runaway
Improve heat dissipation and check temperature coefficient
Value drift
Monitor operating temperature and verify power derating
Physical damage
Inspect mounting, reduce mechanical stress, improve protection
Quick Reference
Power Formulas
- P = V × I
- P = V² / R
- P = I² × R
Temperature Derating
- -4% per °C above 25°C
- Maximum temperature: 70°C
- Thermal resistance: 100°C/W
Common Values
- 0.125W (1/8W)
- 0.25W (1/4W)
- 0.5W (1/2W)
- 1W
- 2W
- 3W
- 5W
Safety Margins
- Use 2x safety factor
- Consider temperature rise
- Account for derating