Polyphase Diode Driver for LED Current Regulation
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Solution Overview
Problem
Existing diode drivers for light emitting diodes (LEDs) are inefficient due to power dissipation in linear pass elements, unsuitable for miniature surface-mount technology, and limited in rise and fall times, requiring large components and excessive energy storage.
Innovation Solution
A polyphase diode driver using multiple staggered-phase switching elements to distribute dissipation and achieve low ripple and fast rise/fall times, allowing for miniature, low-cost, high-efficiency constant current supply to LEDs, including laser diodes, by sharing inductor and switching losses across multiple stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear pass element is used to regulate current through LEDs, then constant current control is achieved, but power dissipation and heat generation occur
Solution Approach 1:
The patent divides the current regulation function into multiple discrete switching elements (transistors Q1-Q4) operating in alternating phases, replacing the single linear pass element. Each switching element handles a portion of the total current duty cycle, enabling regulation through pulsing rather than continuous linear operation, thereby eliminating the power dissipation inherent in linear regulation.
Solution Approach 2:
The patent implements periodic switching action where transistors Q1 and Q2 operate in alternating phases to drive the LED string. By periodically switching the current on and off with appropriate duty cycles, the system achieves average current control without the continuous power dissipation of linear regulation, converting the regulation mechanism from dissipative to switching-based.
2Power
If a single-phase switching controller is used, then power conversion is achieved, but large inductor values and heat sinks are required
Solution Approach 1:
The patent segments the power conversion function across multiple switching phases (at least two phases with alternating transistors). By distributing the current handling across multiple switches and inductors operating in sequence, each individual inductor can be smaller while the combined output provides the required current, eliminating the need for large single-phase filtering components.
Solution Approach 2:
The patent merges multiple phase outputs into a single combined LED drive current. By combining the outputs of multiple switching phases that operate alternately, the system achieves smooth current delivery with reduced ripple, allowing smaller inductor values compared to single-phase designs while maintaining power conversion efficiency.
3Reliability
If a linear current regulator is used with energy storage capacitor, then constant current is maintained, but large capacitance values are needed to minimize voltage droop
Solution Approach 1:
The patent uses periodic switching action to recharge the energy storage capacitor at a high frequency during the off-phase of LED current delivery. By continuously replenishing the capacitor with switched current pulses, the system maintains constant LED current without requiring large capacitance values, as the capacitor is rapidly recharged between discharge cycles.
Solution Approach 2:
The patent ensures continuous operation by alternating between multiple switching phases while one phase is discharging current to the LED string. The complementary phase simultaneously recharges the energy storage capacitor, maintaining continuous useful action without interruption. This continuous cycling eliminates the need for large capacitors that would be required to sustain current during long discharge intervals.
4Ease of operation
If conventional switching elements are used, then current control is achieved, but rise and fall times are limited
Solution Approach 1:
The patent segments the current control function across multiple switching elements that can be independently controlled. By dividing the total current duty cycle among multiple transistors (Q1-Q4), each switching element operates at reduced stress and can achieve faster switching transitions. The segmented approach allows optimized gate drive signals for each switch, improving rise and fall times compared to single-element control.
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 polyphase driver provides efficient, constant, pulsed, or variable current to LEDs with reduced ripple and smaller component sizes, overcoming the inefficiencies and size limitations of traditional drivers, while minimizing energy storage requirements.
Implementation Method 1
An inductor (L) is connected between the switching device and the output of the driver stage. When the switching device is turned ON current through the inductor rises, when the inductor current reaches the value of a demanded current the switch is turned OFF, and after the switch is turned OFF the inductor continues to supply (output) current to the load
Implementation Method 2
A rectifying device (D) connected between the inductor and the supply line allows current to continue to flow in the inductor and be supplied to the load after the switch is turned off
Data Source
AI summary
A driver supplying a total current to a load has a plurality (n) of driver stages (ST1 . . . STn). One stage is a master stage. Each driver stage has a switching device (Q) and an inductor (L) connected in series between the switching device and the output of the driver stage. The switching devices are turned ON in sequence with one another, during a cycle time (Tc) which is determined by sensing current through the inductor (L1) in the master stage. When the switching device is turned ON current through the inductor rises, when the inductor current reaches the value of a demanded current the switch is turned OFF, and after the switch is turned OFF the inductor continues to supply (output) current to the load with a current which ramps down. A rectifying device (D) connected between the inductor and the supply line allows current to continue to flow in the inductor and be supplied to the load after the switch is turned OFF.