Saturable Inductor for Parallel Power Switch Inrush Current
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Solution Overview
Problem
In power switching circuits with parallel power switches, the initial switch turns on first and experiences inrush current overload, leading to potential overheating and destruction, while existing solutions fail to ensure simultaneous turn-on of all switches, radiation hardness, and low power dissipation without increased complexity or cost, especially in high-reliability space applications.
Innovation Solution
Incorporating a saturable inductor in series with parallel power switches, which saturates over a specific time period, delaying inrush current and minimizing inductance contribution during load transients, thus protecting switches and the power bus from high peak voltages and currents, while allowing all switches to turn on simultaneously.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a normal inductor is used to delay inrush current, then inrush current is reduced, but inductance contributes to LC resonance causing high peak voltages and currents during load transients
Solution Approach 1:
The inductor uses a saturable core material that dynamically changes its inductance based on the current level. At low currents (inrush phase), the core is unsaturated and provides high inductance to limit current. As current increases, the core saturates and inductance drops to a low value (31 nH), eliminating LC resonance during normal operation. This dynamic property allows the inductor to adapt its behavior to different operating conditions.
Solution Approach 2:
The inductance parameter of the inductor is changed from a fixed value to a variable value through core saturation. The saturable core material causes the inductance to transition from a high value (limiting inrush current) to a low value (31 nH during steady state), effectively changing the electrical parameters of the circuit based on operating conditions and resolving the contradiction between inrush current limitation and LC resonance prevention.
2Power
If parallel power switches are used to handle high current, then current capacity is increased, but one switch turns on first causing inrush current overload and potential destruction
Solution Approach 1:
The saturable inductor is placed in series with the parallel power switches to perform preliminary action by limiting the inrush current before it reaches the switches. The high inductance of the unsaturated core prevents excessive current from flowing into the switches during turn-on, protecting them from overload while allowing them to share current equally once the inductor saturates.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces peak inrush current and power dissipation by 90% and 99%, respectively, while maintaining low inductance during steady-state operation, ensuring all switches turn on safely and minimizing bus ringing, thus addressing the need for simultaneous turn-on and radiation hardness without added complexity or cost.
Implementation Method 1
The saturable inductor includes a core made of a saturating core material which saturates over a time period between about 10 microseconds and about 100 microseconds to an inductance of about 31 nH
Data Source
AI summary
Embodiments described herein are directed to power switching circuits having a saturable inductor. In one embodiment, a power switching circuit includes a power switch assembly operable to be connected to a power source. The power switch assembly includes a plurality of parallel power switches connected to and receiving current from the power source and a saturable inductor electrically coupled in series with the plurality of parallel power switches.