LED String Driving Circuit with Shared Current Regulation
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Solution Overview
Problem
Existing LED driving circuits face inefficiencies and increased power losses due to varying turn-on voltage drops across LED strings, leading to high costs and reduced efficiency, especially when using independent current regulating circuits for each string.
Innovation Solution
A constant current driving circuit that includes a voltage regulator, multiple current regulating circuits, a voltage feedback circuit, and signal generating circuits to regulate currents and voltage drops across LED strings, using a minimum terminal voltage selector and error amplifying circuit to generate reference current and duty cycle signals for optimal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If independent current regulating circuits are used for each LED string, then current control precision is improved, but power loss increases and device complexity increases
Solution Approach 1:
The patent merges multiple independent current regulating circuits into a single shared current regulating circuit that serves multiple LED strings. Instead of having separate LDO regulators for each string, the invention uses one common regulator with multiple output terminals connected to different LED strings, thereby reducing the number of components and minimizing power losses associated with multiple independent regulation circuits.
Solution Approach 2:
The shared current regulating circuit is designed to perform multiple functions by regulating current for multiple LED strings simultaneously through a single circuit architecture. The circuit uses a current sampling resistor and error amplifier to control the current flowing through all LED strings, making the single circuit serve the purpose of multiple separate circuits would otherwise be needed.
2Measurement precision
If independent current regulating circuits are used for each LED string, then current control precision is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple independent current regulating circuits into a single shared current regulating circuit that serves multiple LED strings. Instead of having separate LDO regulators for each string, the invention uses one common regulator with multiple output terminals connected to different LED strings, thereby reducing the number of components and minimizing power losses associated with multiple independent regulation circuits.
3Device complexity
If LED strings with different turn-on voltage drops are connected in parallel, then circuit complexity is reduced, but current distribution uniformity deteriorates
Solution Approach 1:
The patent implements a feedback mechanism using a current sampling resistor connected in series with the LED strings and an error amplifier that monitors the current flowing through the strings. The error amplifier compares the voltage across the sampling resistor with a reference voltage and adjusts the gate voltage of the PMOS transistor accordingly, providing negative feedback to equalize current distribution across LED strings with different turn-on voltage drops.
Solution Approach 2:
The patent dynamically adjusts the gate voltage parameter of the PMOS transistor based on feedback from the error amplifier. By changing the gate voltage parameter in response to detected current variations, the circuit compensates for differences in turn-on voltage drops among LED strings and maintains uniform current distribution across all strings.
Data Source
AI summary
A constant current driving circuit can include: LED strings; a voltage regulator configured to provide an output voltage signal as a supply for the LED strings; current regulating circuits corresponding to the LED strings, and being coupled between the LED strings and ground, where the current regulating circuits are configured to regulate currents through the LED strings according to present currents and reference current signals; a voltage feedback circuit configured to receive input voltage signals of the current regulating circuits, and to select a voltage feedback signal for controlling the output voltage signal according to the voltage feedback signal and a reference voltage signal; and a signal generating circuit corresponding to the current regulating circuits, where each signal generating circuit receives an input voltage signal of a corresponding current regulating circuit, and generates an error amplifying signal according to the input voltage signal and the reference voltage signal.