Isolated LED Driver Circuit With Capacitive Switch Protection
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Solution Overview
Problem
Existing LED driver circuits lack effective and cost-efficient protection mechanisms for semiconductor switches, particularly in cases of control circuit failures, which can lead to overheating and failure to meet safety standards, especially in emergency lighting applications.
Innovation Solution
An electrically isolated LED driver circuit incorporating a control circuit, a semiconductor element, and at least one capacitive element to couple and isolate the primary and secondary sides, enabling safe and cheap control of semiconductor switches over a galvanically separated barrier, using capacitors to prevent permanent switching on during failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transformer is used to control a semiconductor switch over a galvanically separated barrier, then the control can be achieved, but the cost, size, and manufacturing complexity increase significantly
Solution Approach 1:
The patent introduces a capacitive coupling circuit as an intermediary element to transfer control signals across the galvanic barrier. The capacitor couples the control circuit output to the semiconductor switch gate, enabling control without direct galvanic connection. This replaces complex transformers or optocouplers with a simple capacitive coupling network, reducing device complexity while maintaining control reliability.
2Device complexity
If optocouplers are used for galvanic separation, then the cost and size are reduced compared to transformers, but aging effects and temperature influences degrade performance
Solution Approach 1:
The patent replaces the optical system (optocoupler) with an electrical capacitive coupling system. Instead of using light transmission through an optical barrier, the invention uses electric field coupling through a capacitor to transfer the control signal. This substitution eliminates the aging effects and temperature influences characteristic of optocouplers while maintaining galvanic isolation, thereby improving control stability.
3Device complexity
If the control circuit directly controls the semiconductor switch without galvanic separation, then the circuit is simpler, but the switch can be damaged by voltage spikes and failures
Solution Approach 1:
The capacitor serves as a galvanic barrier that isolates the control circuit from the power circuit while still allowing control signal transmission. This intermediary element prevents voltage spikes and failures in the power circuit from directly affecting the control circuit and damaging the semiconductor switch, while adding minimal complexity to the overall system.
4Reliability
If the semiconductor switch is protected with complex protection circuits, then the reliability improves, but the cost and manufacturing complexity increase
Solution Approach 1:
The capacitive coupling circuit provides inherent protection against voltage spikes and overvoltage conditions while using simple, inexpensive components. The capacitor naturally blocks DC voltage and high-frequency noise, providing protection without requiring complex active protection circuits. This approach improves switch reliability while maintaining ease of manufacture.
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 provides a fail-safe, cost-effective protection mechanism that prevents overheating and ensures compliance with safety standards by using capacitive elements to decouple control signals, allowing for efficient and reliable operation of LED driver circuits.
Implementation Method 1
at least one capacitive element (103) configured to couple a primary side and a secondary side in an electrically isolated manner
Implementation Method 2
a semiconductor element configured to enable discharging of the at least one capacitive element
Data Source
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AI summary
The present invention relates to the field of lighting devices and to light emitting diode (LED) driver circuits, wherein a switch or a secondary side of an LED driver circuit is protected, e.g. in case of failure of the driver circuit. The present invention therefore provides an electrically isolated LED driver circuit 100, comprising a control circuit 101 at a primary side of the LED driver circuit 100, a switch 102 at a secondary side of the LED driver circuit 100, a semiconductor element and at least one capacitive element 103; wherein the control circuit 101 is configured to control the switch 102 in a cycled manner; wherein the at least one capacitive element 103 is configured to couple the primary side and the secondary side in an electrically isolated manner and wherein the semiconductor element is in particular configured to enable discharging of the at least one capacitive element 103.