Fairchild Power Switch(FPS)# Technical Documentation: KA5L0380 Power Switching IC
## 1. Application Scenarios
### 1.1 Typical Use Cases
The KA5L0380 is a high-voltage power switching integrated circuit designed for offline switch-mode power supplies (SMPS). Its primary use cases include:
Primary Applications:
- Flyback Converters : Most commonly implemented in isolated flyback topologies for AC-DC conversion
- Quasi-Resonant Operation : Supports valley switching for reduced switching losses and improved EMI performance
- Standby Power Supplies : Low-power auxiliary supplies in larger systems
- Battery Chargers : For consumer electronics and small appliances
### 1.2 Industry Applications
Consumer Electronics:
- LCD/LED TV power supplies (typically 30-60W range)
- Set-top boxes and cable modems
- DVD/Blu-ray players and audio systems
- Printer and scanner power modules
Industrial Applications:
- Industrial control power supplies
- Measurement equipment auxiliary supplies
- Low-power motor control circuits
IT Equipment:
- Desktop computer standby power supplies
- Monitor power boards
- Network equipment (routers, switches)
### 1.3 Practical Advantages and Limitations
Advantages:
- Integrated Design : Combines high-voltage MOSFET (800V/3A), PWM controller, and protection circuits in a single TO-220F package
- Low Standby Power : Typically achieves <100mW standby consumption with proper design
- Built-in Protection : Includes over-current protection (OCP), over-temperature protection (OTP), and over-voltage protection (OVP)
- Soft-start Function : Reduces inrush current during startup
- Frequency Jittering : Reduces EMI emissions for easier compliance testing
Limitations:
- Power Range : Limited to approximately 60W maximum output (depending on topology and thermal design)
- Fixed Frequency Operation : Lacks advanced frequency modulation features of newer devices
- Thermal Considerations : TO-220F package requires adequate heatsinking at higher power levels
- Efficiency : May not meet highest efficiency standards compared to newer resonant converters
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Thermal Management
- Problem : Overheating leading to thermal shutdown or reduced reliability
- Solution : Ensure sufficient PCB copper area (≥100mm²), proper heatsinking, and adequate airflow
Pitfall 2: EMI Compliance Issues
- Problem : Excessive conducted and radiated emissions
- Solution : Implement proper input filtering, use Y-capacitors appropriately, optimize transformer construction, and utilize the IC's frequency jitter feature
Pitfall 3: Startup Failures
- Problem : Insufficient startup current or voltage
- Solution : Ensure startup resistor provides adequate current (typically 1-2mA) and startup capacitor value is appropriate (22-47μF)
Pitfall 4: Over-current Protection Malfunction
- Problem : False triggering or failure to trigger
- Solution : Properly calculate current sense resistor value and ensure clean layout of sense circuitry
### 2.2 Compatibility Issues with Other Components
Transformer Design:
- Must be specifically designed for quasi-resonant operation
- Proper leakage inductance control is critical (typically <3% of primary inductance)
- Secondary winding arrangement affects cross-regulation in multiple output designs
Output Rectification:
- Fast recovery diodes required (trr < 75ns)
- Schottky diodes recommended for low-voltage outputs (<20V)
Feedback Circuit:
- Compatible with standard optocouplers (PC817, LTV-817 series)
- TL431 reference IC commonly used for voltage regulation
- Ensure proper compensation network for stability
