LED Driver Leakage Protection via Current Sensor Testing
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Solution Overview
Problem
The risk of electric shock to individuals is increased when retrofit LED tubes, which integrate electronics, are connected directly to AC mains without isolation transformers, as existing solutions primarily focus on overcurrent protection rather than preventing electric shock.
Innovation Solution
An electronic driver with a converter circuit, a series cascade of a current sensor and a solid-state switch, and an electronic controller that tests the connection to the external voltage source to ensure safe operation by measuring return currents and controlling the switch to prevent electric shock, using a unipolar voltage source and local ground node to manage power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an isolation transformer is not installed between AC mains and output ports for cost saving, then device complexity and cost are reduced, but the risk of electric shock to personnel increases
Solution Approach 1:
The system performs preliminary testing before enabling full operation. A test subprocess is executed that activates the solid-state switch for a limited test duration to detect improper connections before the LED load operates, preventing electric shock hazard while maintaining simplicity
Solution Approach 2:
A current sensor is introduced as an intermediary element to monitor the return current. This mediator detects the electrical connection status without requiring an isolation transformer, enabling safe operation by providing feedback about the connection state
2Object-affected harmful factors
If a test subprocess is executed to detect improper connections, then electric shock protection is improved, but the operation time increases due to testing duration
Solution Approach 1:
The test subprocess uses partial action by limiting the test duration to a maximum value that is sufficient for detection but not excessive. The solid-state switch is activated only for the minimum necessary time to perform the safety check, balancing protection with time efficiency
Solution Approach 2:
The testing is performed periodically at specific moments (before operation and after idle period) rather than continuously. This periodic approach provides necessary safety checks while minimizing the time the system is non-operational
3Difficulty of detecting and measuring
If the solid-state switch is switched on for testing, then connection detection capability is improved, but energy consumption increases during test duration
Solution Approach 1:
The test duration is carefully selected to be the minimum time required to detect improper connections and assess energy within safe limits. This partial action approach provides sufficient detection capability while minimizing unnecessary energy consumption during the test phase
Data Source
AI summary
In a LED driver with electric-leakage protection, a series cascade of a current sensor and a solid-state switch connects a converter circuit to a unipolar voltage source powered by an external voltage source connected to the driver through two electrical contacts. The current sensor measures a return current returned from the converter circuit to the unipolar voltage source. The switch isolates the unipolar voltage source from the converter circuit for electric-shock prevention when the external source is determined not connected to both contacts. To determine it, the switch is switched on for a test duration to drive the converter circuit. This duration is not greater than a maximum test duration predetermined to avoid a person absorbing an energy greater than a pre-defined human-tolerable shock energy when the person accidentally touches one of the contacts. Whether the external source is connected to both contacts is determined according to the return current.