LED Drive Circuit Switching Series Parallel for Uniform Usage
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Solution Overview
Problem
Existing LED drive circuits experience uneven usage of LED loads, leading to reduced lifetime and low utilization due to variations in operating time among the loads.
Innovation Solution
An LED drive circuit design that switches N+1 LED loads between parallel and series connections using N first and N second transistors, along with a third transistor to regulate current, ensuring equal current flow and prolonged usage time by controlling the transistors' states based on input voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If LED loads are directly connected to LDO linear voltage regulator with fixed series connection, then circuit structure is simple, but usage time of LED loads is uneven and lifetime is reduced
Solution Approach 1:
The patent applies dynamics by making the LED load connection configuration changeable between series and parallel states. The control unit dynamically switches between different connection modes based on input voltage levels, transforming a static circuit into a dynamic one that adapts to varying conditions, thereby equalizing usage time across all LED loads and extending overall lifetime.
Solution Approach 2:
The patent implements periodic action through cyclic switching between series and parallel connection modes. The control unit periodically changes the connection configuration in response to input voltage variations, creating a rhythmic operational pattern that distributes stress evenly across LED loads over time, preventing any single load from being overused.
2Device complexity
If LED loads are connected in series, then current regulation is simple, but absolute usage time is shortened resulting in low utilization
Solution Approach 1:
The patent applies segmentation by dividing the LED loads into multiple groups that can be independently connected in series or parallel. The control unit segments the overall LED string into manageable sections, allowing flexible reconfiguration based on voltage conditions, thereby increasing total operational time and utilization without requiring complex individual control of each LED.
Solution Approach 2:
The patent utilizes parameter changes by altering the connection configuration (series/parallel) in response to input voltage parameter variations. When input voltage changes, the control unit adjusts the effective resistance and current distribution by changing connection parameters, optimizing utilization across different operating conditions.
3Measurement precision
If transistors operate in linear state to regulate current, then current control is precise, but power loss increases and efficiency decreases
Solution Approach 1:
The patent reduces power loss by using periodic switching action instead of continuous linear regulation. The transistors switch between on and off states in periodic cycles, with duty cycle adjustment providing current control. This pulse-width modulation approach maintains precision while minimizing the time transistors spend in the high-power-dissipation linear region.
Solution Approach 2:
The patent transitions from static linear regulation to dynamic switching control. The control unit dynamically adjusts switching frequency and duty cycle based on voltage conditions, allowing the system to operate efficiently across varying input voltages while maintaining precise current control only when necessary, thereby reducing overall power loss.
Data Source
AI summary
Disclosed an LED drive circuit, which is configured to switch the connection of a plurality of LED loads between parallel connection and series connection. When an input voltage is low, the LED loads are controlled to be in parallel connection, and the transistors provided on corresponding parallel branch circuits are controlled to operate in a linear state for regulating the current flowing through the parallel branch circuits. When the input voltage increases, the LED loads or LED drive modules are controlled to be in series connection, and the transistors provided on the series branch circuits are controlled to regulate the current flowing through all the LED loads. Accordingly, on one hand, all the LED loads have a same operating time, on the other hand, all the LED loads operate during most time of every operating cycle, which improves the lifetime of the circuit and the utilization of the LED loads.