Power Management Design Guidelines
Power Supply Selection
Power supply selection considers output voltage/current, input voltage range, efficiency, size, and safety requirements. Lite-On offers solutions from 5W to 150W with various form factors. Modular designs offer faster time-to-market compared to discrete designs.
Thermal Design Considerations
Thermal design is critical for reliability. Calculate power dissipation: Pd = Pin - Pout = Pout × (1/η - 1). For 90% efficiency at 50W output: Pd = 50W × (1/0.9 - 1) = 5.6W. Ensure adequate heat sinking or airflow to keep internal temperatures within ratings.
Input and Output Filtering
Input filtering reduces conducted EMI and protects against input transients. Output filtering reduces ripple and noise. Follow manufacturer recommendations for capacitor types and values. Ceramic capacitors for high frequency, electrolytic for bulk storage.
Protection Features
Modern power supplies include comprehensive protection: Over-voltage protection (OVP) prevents output overvoltage, Over-current protection (OCP) limits output current, Over-temperature protection (OTP) prevents thermal damage, Short-circuit protection (SCP) handles output shorts.
EMC Compliance
EMC compliance requires attention to both conducted and radiated emissions. Input filtering, proper PCB layout, shielding, and snubber circuits all contribute to EMC performance. Lite-On power modules are designed and tested for standard EMC requirements.
💡 FAE Insights
Technical Logic
Power supply design balances efficiency, size, cost, and reliability. Integrated modules offer best time-to-market for standard requirements. Custom designs may be justified for high volumes or special requirements.
Key Considerations
Thermal design is often the limiting factor. Plan for worst-case conditions including high ambient temperature and low airflow. Protection features must be coordinated with system-level protection.
📋 Customer Cases
Medical Device Manufacturer
Challenge
Needed compact, efficient power supply with medical safety ratings
Solution
Implemented Lite-On medical-grade power module with custom thermal design
Customer Feedback
"Excellent support during certification process"
Frequently Asked Questions
1. How do I calculate power dissipation?
Power dissipation is the difference between input and output power. Formula: Pd = Pout × (1/η - 1), where η is efficiency. For example, 100W output at 90% efficiency: Pd = 100W × (1/0.9 - 1) = 11.1W. This heat must be dissipated through convection, conduction, or radiation.
2. What is the difference between linear and switching regulators?
Linear regulators are simple, low noise, but inefficient (dissipate excess voltage as heat). Switching regulators are efficient (80-95%) but more complex with higher noise. Linear suits low drop-out, noise-sensitive applications. Switching is preferred for high efficiency and large voltage differences.
3. How do I reduce EMI in power supply design?
EMI reduction techniques: Proper input filtering with X and Y capacitors, snubber circuits on switching nodes, proper PCB layout with minimized loop areas, shielding for sensitive applications, soft-start to reduce inrush current, spread spectrum for clocked converters.
4. What is hold-up time and why does it matter?
Hold-up time is how long output voltage remains within regulation after input power is lost. Important for systems needing time to save data or switch to backup power. Typical hold-up is 10-20ms at full load. Increasing input capacitance extends hold-up time.
5. Can I parallel power supplies for higher current?
Parallel operation requires power supplies designed for current sharing. Simply connecting outputs in parallel usually results in uneven current distribution. Some Lite-On modules support parallel operation with proper configuration. Contact FAE for parallel operation guidance.