How to design a diode parallel structure in a redundant energy system?

一, Device selection: Scene based parameter matching
1. Current capacity and discreteness control
Redundant systems need to cope with single module failure scenarios, and parallel diodes need to meet the following requirements:

Rated current redundancy: The rated current of a single tube should be ≥ the maximum load current of the system/(number of parallel connections x 0.8), with a 20% safety margin reserved. For example, in a 48V/20A system where 4 pipes are connected in parallel, a single pipe model of 30A or higher should be selected.
Forward voltage drop consistency: The Vf dispersion of Schottky diodes should be ≤ 5% to avoid current distribution imbalance caused by differences in conduction voltage drop. In a new energy vehicle OBC case, four 30A Schottky diodes with a Vf deviation of ± 0.1V were connected in parallel, and a 0.2 Ω current sharing resistor was used to achieve a current deviation of<± 5% in the entire temperature range.
2. Reverse characteristics and protection requirements
Reverse withstand voltage margin: The diode VRRM needs to be ≥ 1.5 times the maximum system voltage. For example, in a photovoltaic grid connected system, the open circuit voltage of the solar panel can reach 1000V, and TVS diodes with VRRM ≥ 1500V need to be selected.
Reverse recovery time optimization: Ultra fast recovery diodes with Trr<50ns should be selected for high-frequency switching scenarios. In a power supply case of a certain communication base station, UF4007 diodes (Trr=35ns) were used instead of ordinary rectifiers to reduce reverse recovery losses by 70%.
二, Topology Design: Balancing Redundancy and Isolation
1. Parallel current sharing architecture
Passive current sharing scheme: Current balancing is achieved by connecting 0.1-0.5 Ω low inductance current sharing resistors in series. A certain industrial PLC power supply adopts a dual tube parallel design, and the backup branch can be connected within 10 μ s when the main tube fails. The power consumption of the current sharing resistor is controlled within 0.5W.
Active current sharing scheme: using active current sharing chips such as LTC4370, dynamic current distribution is achieved by adjusting the gate voltage. In a data center power supply case, a 4-tube parallel system achieved load current distribution error<± 2% through active current sharing control.
2. Redundant isolation design
N+1 redundant topology: The main module and backup module are isolated by diodes to ensure that a single module failure does not affect the system output. The power supply of a certain medical equipment adopts a 3+1 redundancy design, and the backup module is isolated from the main circuit through diodes, with a fault switching time of less than 50 μ s.
Back to back MOSFET replacement solution: In scenarios that require bidirectional isolation, two N-channel MOSFETs are connected back-to-back and combined with the LTC4416 control chip to achieve low loss isolation. In a server power supply case, this solution reduced the conduction voltage drop from 0.45V to 0.03V, resulting in a 12% increase in efficiency.
三, Thermal management: synergy between heat dissipation and reliability
1. Power consumption calculation and heat dissipation design
Calculation of conduction loss: P=Vf × Iavg, low Vf diodes should be prioritized for high current scenarios. For example, under a current of 12A, the power consumption of a 0.45V Schottky diode reaches 5.4W, and a heat sink needs to be installed; The 0.3V SiC Schottky diode has a power consumption of only 3.6W and can dissipate heat naturally.
Thermal resistance control: Using low thermal resistance packaging (such as TO-220 packaging with R θ JA=40 ℃/W), combined with thermal conductive silicone grease to control the junction temperature below 125 ℃. In a case study of an electric vehicle charging module, the diode temperature rise was reduced from 45 ℃ to 25 ℃ by optimizing the PCB copper foil area (≥ 100mm ²/A).
2. Layout optimization and parasitic parameter suppression
Parasitic inductance control: When PCB layout, the length of diode pin routing should be<5mm to avoid the formation of oscillation circuits. In a certain photovoltaic inverter case, by arranging parallel diodes on the same side of the PCB, the parasitic inductance was reduced from 12nH to 2nH, and the reverse recovery overshoot voltage was reduced by 60%.
Thermal coupling design: In high power density scenarios, a common heat sink design is used to ensure temperature balance of parallel diodes. In a certain communication power supply case, the junction temperature deviation was reduced from 15 ℃ to 5 ℃ by installing four diodes tightly against the heat sink.
四, Engineering verification: closed-loop from simulation to actual measurement
1. Simulation verification
SPICE model simulation: Establish an LTspice model for diode parallel circuits to verify the current sharing effect and thermal distribution. In a certain aviation power supply case, it was found through simulation that there was a 20% current imbalance in parallel diodes. After optimizing the current sharing resistance parameters, the imbalance was reduced to 5%.
Thermal simulation analysis: FloTHERM and other tools are used to simulate the heat dissipation path and optimize the structure of the heat sink. In a case study of a rail transit power supply, the height of the heat sink fins was adjusted from 15mm to 20mm through simulation, reducing the maximum junction temperature from 130 ℃ to 115 ℃.
2. Reliability testing
HALT testing: Verify design limits through high acceleration life testing. In a military power supply case, the diode parallel structure did not fail after 1000 cycles of temperature cycling from -40 ℃ to+125 ℃.
EMC testing: Verify whether the noise generated by diode reverse recovery meets the standard. In a case study of a medical device power supply, a 100pF capacitor was connected in parallel across the diode to reduce radiated interference from 45dB μ V to 35dB μ V.
五, Typical application cases
1. Redundant power supply for communication base stations
Using 4 parallel 20A power supplies, each isolated by SR1660 Schottky diodes (16A/60V). Realize high reliability through the following design:

Selection of current sharing resistor: 0.3 Ω/5W cement resistor, ensuring that the single tube current does not exceed 15A
Heat dissipation design: heat sink area ≥ 200cm ², junction temperature<110 ℃ under natural heat dissipation conditions
Protection function: TVS diode (18V/1kW) suppresses surges, varistor (150V) prevents overvoltage
2. Charging module for new energy vehicles
Replacing traditional diodes with SiC MOSFETs to achieve low loss redundancy:

Topology: back-to-back C2M0080120D SiC MOSFET (1200V/80m Ω)
Control scheme: LTC4416 driver, with a conduction voltage drop of only 0.1V
Efficiency improvement: Compared to Schottky diode solutions, the system efficiency has increased from 92% to 96%