LED Buck PFC Switching-Time Detection Without Level Shifters
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Solution Overview
Problem
Existing LED fixtures with Buck power factor control circuits cannot directly interpret ELV LED drive signals without expensive components like optocouplers, preventing them from accepting ELV control and delivering usage data to manufacturers.
Innovation Solution
A controller referenced to the output ground of the Buck PFC circuit measures switching times to determine input signal characteristics like voltage, frequency, and phase angle without a level shifter, using the switching signal of components like the Buck inductor or freewheeling diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Buck power factor control circuit is used in LED fixtures, then common-mode noise is reduced and efficiency is improved, but the microcontroller cannot directly read the input voltage without a level-shifter
Solution Approach 1:
The patent introduces an intermediary measurement approach by measuring the switching times of the Buck PFC circuit's internal components (MOSFET, diode, or inductor) as a mediator between the input voltage and the microcontroller. This switching time measurement serves as an indirect indicator of input voltage characteristics without requiring direct voltage measurement across ground potential differences.
Solution Approach 2:
The patent replaces the traditional electrical measurement system (voltage measurement with level-shifters or optocouplers) with a timing-based measurement system. By measuring the duration of switching events in the Buck PFC circuit, the system substitutes direct electrical potential measurement with temporal measurement, eliminating the need for level-shifting circuitry.
2Ease of operation
If optocouplers are used to enable the microcontroller to read input voltage, then voltage interpretation is possible, but system cost increases
Solution Approach 1:
The patent utilizes existing, inexpensive components within the Buck PFC circuit (MOSFET, diode, or inductor) whose switching behavior can be measured. Instead of adding expensive optocouplers, the system repurposes the timing characteristics of these already-present components for the dual purpose of power conversion and input voltage sensing.
Solution Approach 2:
The Buck PFC circuit's own switching components provide the measurement signal needed for input voltage detection. The circuit's internal operation generates timing information that directly reveals input voltage characteristics, allowing the system to sense its own operating conditions without external sensing components.
3Productivity
If digitally-dimmed white fixtures are used, then design-to-market time is reduced, but ELV compatibility is lost
Solution Approach 1:
The patent enables the digitally-controlled LED fixture to perform multiple functions: it maintains its digital control capabilities while also gaining the ability to interpret ELV dimming signals through phase angle detection. By measuring switching times and calculating phase angles, the fixture can adapt to both digital and ELV control schemes, making it universally compatible with different control systems.
Data Source
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AI summary
An LED power supply (100) configured to detect a characteristic of an input signal, includes a Buck power factor control circuit (D1, U1, Q1, D2, L1, C1) being configured to receive an input signal, the input signal (VAC) being referenced to a power ground, and to output an output signal, the output signal (Vout) being referenced to an output ground, wherein the output ground is level shifted with respect to the power ground; and a controller (106) configured to output an LED drive signal, the controller referenced to the output ground, wherein the controller is configured to determine the characteristic of the input signal according to a switching time of the Buck power factor control circuit, the switching time of the Buck power factor control circuit being determined by the controller according to a switching signal referenced to the output ground.