How to protect diodes in high temperature and high humidity energy equipment?

一, Material selection: Suitable for devices that are resistant to moisture, heat, and high temperatures
1. Optimization of packaging materials
In high temperature and high humidity environments, traditional epoxy resin packaging is prone to delamination or popcorn effect due to water vapor infiltration. Industrial grade diodes are packaged in silicone or ceramic, which can significantly improve their resistance to moisture and heat. For example, a certain photovoltaic inverter project selected ceramic encapsulated Schottky diodes. After continuous operation for 1000 hours in the double 85 test (85 ℃/85% RH), there was no delamination phenomenon inside the package, while ordinary epoxy resin encapsulated devices exploded after 500 hours.

2. Chip process upgrade
For high-temperature environments, chips with low leakage current characteristics should be selected. For example, using silicon carbide (SiC) diodes can significantly reduce reverse leakage current at high temperatures. Comparative testing of a certain offshore wind power converter project shows that at a junction temperature of 125 ℃, the reverse leakage current of SiC diodes is reduced by 80% compared to silicon-based diodes, and the system efficiency is improved by 2.3%.

3. Principles of derating design
In high-temperature scenarios, diodes need to be de rated according to their actual operating temperature. For example, if the rated reverse voltage of the device is 60V, it is recommended to choose a withstand voltage level of 100V or higher at 85 ℃ to reserve safety margin. A certain energy storage system project reduced the device failure rate from 5% to 0.3% by increasing the diode withstand voltage level from 60V to 100V.

二, Structural Design: Thermal Management and Isolation Protection
1. Strengthen the heat dissipation structure
Copper foil expansion: In PCB layout, increasing the copper foil area enhances heat conduction. A certain photovoltaic controller project expanded the copper foil area under the diode from 10mm ² to 50mm ², reducing the junction temperature by 15 ℃.
Integrated heat sink: High heat dissipation efficiency packages such as DFN and TO-220 are used in conjunction with heat sinks. For example, a certain industrial UPS project uses TO-220 packaged diodes and installs aluminum heat sinks to control the junction temperature within 120 ℃ during full load operation.
Application of thermal pad: Filling thermal grease or thermal pad between diode and heat sink can reduce contact thermal resistance. Tests have shown that using a 0.5mm thick silicone thermal pad can reduce the thermal resistance from 2 ℃/W to 0.8 ℃/W.
2. Electrical isolation design
Parallel connection of current sharing resistors: When multiple diodes are connected in parallel, a low resistance current sharing resistor (such as 0.1 Ω) should be connected in series to each diode to avoid uneven current distribution due to differences in forward voltage drop. A certain energy storage battery balancing circuit project has reduced the current deviation of parallel diodes from 30% to within 5% through this design.
Reverse protection diode: Connecting reverse diodes in parallel at both ends of the main diode can prevent the main diode from breaking down when the reverse voltage is too high. For example, a certain electric vehicle charging module project adopts this scheme, which shortens the response time of reverse overvoltage protection to 10ns.
三, Environmental Control: Microenvironment Isolation and Ventilation Optimization
1. Enhancement of protection level
IP protection standard: Select equipment with IP65 (dustproof and waterproof) or IP67 (waterproof) rating based on environmental humidity. A certain offshore drilling platform project uses IP67 protective diode modules, which have not experienced corrosion after continuous operation in salt spray environment for 3 years.
Control cabinet integration: Place the diode module in a sealed control cabinet and install air conditioning or heat exchangers to regulate temperature and humidity. For example, a UPS project in a data center uses a control cabinet to keep the internal temperature below 40 ℃ and humidity within 50% RH, thereby extending the lifespan of diodes by 40%.
2. Optimization of ventilation system
Forced air cooling design: In power intensive applications, fans are used for forced ventilation. A certain photovoltaic inverter project optimized the air duct design to increase the air flow velocity around the diode to 3m/s and reduce the junction temperature by 20 ℃.
Natural convection enhancement: In low-power scenarios, increasing the spacing or tilt angle of the heat sink fins can improve the efficiency of natural convection. Tests have shown that increasing the spacing between fins from 2mm to 5mm improves heat dissipation efficiency by 15%.
四, Monitoring and Protection: Real time Feedback and Active Intervention
1. Temperature monitoring system
Thermistor integration: Install NTC thermistor near the diode to monitor junction temperature in real-time. A certain energy storage battery management system project, through this scheme, automatically triggers current limiting protection when the junction temperature exceeds 125 ℃ to avoid thermal runaway.
Infrared temperature measurement technology: using infrared sensors to non-contact monitor the surface temperature of diodes. For example, a wind power inverter project achieves precise control of junction temperature error ± 2 ℃ through infrared temperature measurement.
2. Overload protection mechanism
Transient Voltage Suppressor (TVS): A TVS diode is connected in parallel at the input of the diode to suppress lightning strikes or switch overvoltages. A certain photovoltaic array project has improved its overvoltage withstand capability from 1kV to 6kV through this design.
Software current limiting algorithm: In digital control systems, the diode current is dynamically adjusted through algorithms. For example, a certain electric vehicle charging station project adopts PID current limiting control to shorten the overload response time to 50ms.
五, Case study: Protection practice of offshore wind power converters
A certain offshore wind power project is located in subtropical waters with an ambient temperature of 45 ℃ and humidity of 90% RH. The original design used ordinary silicon-based diodes, and the failure rate after one year of operation was as high as 12%. The improvement plan includes:

Device upgrade: replaced with SiC diode, temperature resistance level increased to 175 ℃;
Heat dissipation enhancement: Adopting DFN packaging and installing copper heat sinks, the junction temperature is reduced from 150 ℃ to 110 ℃;
Environmental isolation: Place the diode module in an IP67 protected control cabinet and install a dehumidification device;
Monitoring and protection: Integrated thermistor and TVS diode to achieve dual protection of temperature and voltage.
After improvement, the system has been running continuously for 3 years without any diode failures, with an 8% increase in annual power generation and a 60% reduction in maintenance costs.