Very fast high-voltage soft-recovery rectifiers# Technical Documentation: BY720 Rectifier Diode
## 1. Application Scenarios
### 1.1 Typical Use Cases
The BY720 is a high-voltage, fast-recovery rectifier diode primarily employed in power conversion circuits where efficient high-frequency rectification is required. Its design makes it particularly suitable for:
- Switching Mode Power Supplies (SMPS) : Used in flyback and forward converter secondary-side rectification circuits operating at frequencies up to 20 kHz
- Voltage Multipliers : Implemented in Cockcroft-Walton voltage multiplier stages for high-voltage DC generation
- Freewheeling/Clamping Circuits : Provides protection for switching transistors by clamping voltage spikes in inductive load applications
- Reverse Polarity Protection : Serves as a blocking diode in DC power input stages
### 1.2 Industry Applications
- Consumer Electronics : Power supply units for televisions, monitors, and audio equipment
- Industrial Controls : Motor drives, welding equipment, and uninterruptible power supplies (UPS)
- Telecommunications : DC-DC converters in base station power systems
- Lighting Systems : Electronic ballasts for fluorescent and HID lighting
- Medical Equipment : High-voltage power supplies for imaging and diagnostic devices
### 1.3 Practical Advantages and Limitations
Advantages:
- Fast Recovery Time : Typical reverse recovery time (trr) of 200 ns minimizes switching losses in high-frequency applications
- High Voltage Rating : Maximum repetitive reverse voltage (VRRM) of 1000V enables use in medium-high voltage circuits
- Robust Construction : Glass-passivated junction provides stable performance across temperature variations
- Low Forward Voltage Drop : Typically 1.3V at rated current reduces conduction losses
Limitations:
- Thermal Management : Maximum junction temperature of 150°C requires adequate heat sinking in high-current applications
- Reverse Recovery Charge : Higher than Schottky diodes, limiting efficiency in very high-frequency circuits (>100 kHz)
- Surge Current Handling : Limited surge capability compared to standard recovery diodes
- Package Constraints : Axial lead package may require additional PCB space compared to surface-mount alternatives
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Thermal Management
- Problem : Overheating due to insufficient heat dissipation in continuous operation
- Solution : Implement proper heat sinking and maintain junction temperature below 110°C for reliability
Pitfall 2: Voltage Spikes Exceeding Ratings
- Problem : Inductive kickback or ringing exceeding VRRM during switching transitions
- Solution : Add snubber circuits (RC networks) across the diode to dampen voltage spikes
Pitfall 3: Reverse Recovery Oscillations
- Problem : Ringing during reverse recovery causing EMI and potential device failure
- Solution : Use series damping resistors (1-10Ω) and minimize parasitic inductance in layout
Pitfall 4: Avalanche Energy Mismatch
- Problem : Repetitive avalanche energy exceeding specified limits in clamping applications
- Solution : Calculate worst-case energy and ensure operation within single-pulse avalanche ratings
### 2.2 Compatibility Issues with Other Components
With Switching Transistors:
- Ensure diode reverse recovery time is compatible with transistor switching speed
- Fast-recovery characteristics of BY720 work well with MOSFETs and IGBTs switching below 50 kHz
With Capacitors:
- Low ESR capacitors recommended in parallel to handle high di/dt during reverse recovery
- Consider capacitor voltage derating when used in voltage multiplier configurations
With Transformers:
- Secondary winding leakage inductance should be minimized to reduce voltage overshoot
- Proper snubber design essential when used with transformers having high leakage inductance
With Control
