Redundant DC Input Circuit Switching for Back-Feed Protection
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Solution Overview
Problem
Existing redundant DC input power supplies face challenges in preventing back-feed currents during single and double fault conditions, which can lead to hazardous exposure when servicing power sources.
Innovation Solution
A back-feed protection circuit is implemented, comprising two redundant input circuits and a control circuit that senses the DC voltages and enables one input circuit while disabling the other to prevent current back-feed, using MOSFETs and diodes in series configurations with a control system to manage switching and prevent back-feed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diodes, relays or MOSFETs are coupled in series along positive and reference rails for back-feed protection, then back-feed protection is provided, but device complexity increases and bulk capacitors with large hold-up capabilities are required
Solution Approach 1:
A control circuit acts as an intermediary between the first and second input circuits, coordinating their operation to prevent back-feed currents. The control circuit enables one input circuit while disabling the other, eliminating the need for complex series-coupled protective devices and large bulk capacitors.
Solution Approach 2:
The control circuit performs multiple functions: it senses voltages from both input circuits, determines which circuit to enable based on voltage levels, and coordinates the enabling/disabling of both input circuits to prevent back-feed. This multi-functional approach replaces multiple dedicated protective components.
2Reliability
If each MOSFET is controlled with its own controller based on drain-source voltage, then back-feed protection is achieved, but device complexity and control circuit requirements increase
Solution Approach 1:
Multiple individual MOSFET controllers are merged into a single control circuit that manages both input circuits. The control circuit senses voltages from both circuits and coordinates their enabling/disabling, replacing the need for separate controllers for each MOSFET and reducing overall control complexity.
Solution Approach 2:
The control circuit uses voltage sensing feedback from both input circuits to make intelligent decisions about which circuit to enable. By continuously monitoring voltage levels and responding to changes, the control circuit prevents back-feed conditions without requiring complex individual MOSFET controllers.
3Duration of action of stationary object
If bulk capacitors with large hold-up capabilities are used when transferring from one input to another, then power supply continuity is maintained, but device complexity and component size increase
Solution Approach 1:
The control circuit performs preliminary voltage sensing and evaluation before transferring between input circuits. By proactively identifying which input circuit should be active based on voltage levels, the control circuit enables smooth transitions without requiring large bulk capacitors to maintain power during switching.
Data Source
AI summary
An electric power supply comprises first and second input circuits for receiving first and second input DC voltages and a control circuit coupled to the first and second input circuits. The control circuit is configured to sense the first input DC voltage and the second input DC voltage and to enable the first input circuit and disable the second input circuit in response to the first input circuit having the highest input DC voltage to substantially prevent current from back feeding to the first input circuit from the second input circuit. The control circuit is also configured to enable the second input circuit and disable the first input circuit in response to the second input circuit having the highest input DC voltage to substantially prevent current from back feeding to the second input circuit from the first input circuit.