AC-DC Power Supply Inrush Suppression With Dynamic Resistor Bypass
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Solution Overview
Problem
Switching power supplies with large bulk capacitors often experience significant inrush currents upon initial activation, which can lead to component damage, trigger circuit breakers, and reduce overall efficiency.
Innovation Solution
Incorporating an inrush current limiting circuit that includes a resistor in series with the bulk capacitor, a relay to bypass the resistor under high load conditions, and a solid-state switching device to bypass the resistor under low load conditions, all controlled by a dedicated control circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a resistor is used to limit inrush current to the bulk capacitor, then inrush current is reduced, but power losses increase under continuous operation
Solution Approach 1:
The patent employs a dynamic bypass mechanism using either a relay or solid-state switching device that changes the circuit configuration based on operating conditions. During startup, the resistor remains in the circuit to limit inrush current. Once the bulk capacitor is charged, the switching device activates to bypass the resistor, eliminating continuous power losses while maintaining inrush protection capability.
Solution Approach 2:
The patent implements preliminary charging of the bulk capacitor through the current-limiting resistor before activating the bypass mechanism. This preliminary action ensures the capacitor is charged to an adequate voltage level before the resistor is removed from the circuit, preventing inrush current issues during subsequent operation while allowing efficient power transfer thereafter.
2Loss of energy
If a relay is used to bypass the resistor under high load conditions, then power losses are reduced, but device complexity increases
Solution Approach 1:
The patent offers an implementation where a solid-state switching device (such as a MOSFET or transistor) replaces the traditional mechanical relay for bypassing the current-limiting resistor. This substitution eliminates mechanical wear, reduces switching noise, improves reliability, and allows for more precise control while achieving the same functional outcome of reducing power losses under continuous operation.
3Reliability
If a solid-state switching device is used to bypass the resistor, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent replaces mechanical relays with solid-state switching devices to eliminate mechanical wear and improve reliability. The solid-state switch can be controlled by simple voltage or current signals, providing reliable operation without moving parts while maintaining relatively simple circuit integration through standard semiconductor components and control logic.
4Loss of energy
If the high power DC-DC converter is selectively enabled under load conditions, then efficiency is improved, but control complexity increases
Solution Approach 1:
The patent implements dynamic load management where the high power DC-DC converter is selectively enabled or disabled based on real-time load conditions. The control circuitry monitors the load and activates the high power converter only when necessary, switching between high power and low power conversion paths to optimize efficiency across varying operating conditions while maintaining manageable control through threshold-based decision logic.
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 limits inrush currents, preventing component damage and reducing power losses, thereby enhancing the efficiency and reliability of switching power supplies, especially during no-load and light-load conditions.
Implementation Method 1
a resistor coupled in series between the one or more input stages and the bulk capacitor so as to limit an inrush current to the bulk capacitor
Implementation Method 2
a solid-state switching device responsive to the control circuitry that selectively bypasses the resistor under low load conditions once the bulk capacitor is charged
Implementation Method 3
a relay responsive to the control circuitry that selectively bypasses the resistor under high load conditions once the bulk capacitor is charged; The relay can have contacts coupled in parallel with the resistor
Data Source
AI summary
A power supply can include a bulk capacitor that receives a DC bus voltage; one or more DC-DC converters that convert the DC bus voltage to a DC output voltage; an inrush current limiting circuit that includes a resistor coupled in series with the bulk capacitor so as to limit an inrush current to the bulk capacitor; and a solid-state switching device that selectively bypasses the resistor once the bulk capacitor is charged; and control circuitry that operates the solid-state switching device to selectively bypass the resistor once the bulk capacitor is charged. The inrush current limiting circuit can further include a relay responsive to the control circuitry that selectively bypasses the resistor under high load conditions once the bulk capacitor is charged; and the control circuitry can further operate the solid-state switching device to selectively bypass the resistor once the bulk capacitor is charged under low load conditions.