Biphase Laser Diode Driver Ripple Cancellation
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Solution Overview
Problem
Existing current drivers for high current laser diodes and LEDs are inefficient due to power dissipation in linear pass elements, leading to high heat generation and the need for large capacitance to minimize voltage droop during pulsed current delivery.
Innovation Solution
A current driver system comprising a master and slave stage, where each stage operates as a buck driver with out-of-phase ripple control, using hysteretic control to minimize ripple and reduce size and complexity, and in digital embodiments, a calibration step determines the faster stage as the master to optimize phase alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If linear dissipative pass elements are used to regulate current, then current control is simple and straightforward, but power dissipation and heat generation increase significantly
Solution Approach 1:
The patent replaces linear dissipative pass elements with a switching regulator system that uses electronic switching (MOSFETs) and magnetic energy storage (inductors) to regulate current. This substitution transforms the current regulation mechanism from resistive dissipation to inductive energy transfer, dramatically reducing power loss while maintaining control capability through pulse-width modulation.
Solution Approach 2:
The patent changes the operating parameters of the regulator by transitioning from continuous linear operation to periodic switching operation. By controlling the duty cycle of the switching elements and utilizing the inductive properties of the transformer, the system achieves current regulation through parameter modulation rather than resistive control, improving efficiency.
2Stability of the object's composition
If large capacitance is used to minimize voltage droop during pulsed current delivery, then voltage stability improves, but device size increases
Solution Approach 1:
The patent employs periodic switching action at high frequency to transfer energy from the input capacitor to the output in small, controlled increments. This periodic energy transfer allows the use of smaller capacitors while maintaining voltage stability, as the high-frequency switching replenishes output energy continuously rather than requiring large bulk capacitance to handle entire pulse energy demands.
Solution Approach 2:
The patent achieves continuous energy transfer through the transformer during both switching states (when primary switch is on and when it is off). This continuous inductive coupling ensures steady energy delivery to the load, reducing voltage droop without requiring oversized output capacitance, as the inductor maintains current flow continuity.
3Device complexity
If single-phase buck driver is used, then device complexity is low, but output ripple is high
Solution Approach 1:
The patent divides the single-phase buck driver into two interleaved half-phases, with each phase contributing alternately to the output current. This segmentation of the switching cycle into two phases operating 180 degrees out of phase reduces the peak-to-peak ripple current by distributing the current delivery across two smaller, alternating pulses, effectively halving the ripple amplitude.
Solution Approach 2:
The patent implements periodic alternating operation of two switching elements (Q1 and Q2) that are driven 180 degrees out of phase. This periodic alternation creates two interleaved current pulses to the output, with the second pulse filling in the valleys of the first pulse, thereby reducing overall output ripple while maintaining the simplicity of the basic buck topology.
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
This approach results in a more efficient current delivery with reduced ripple, lower size, and simplicity, maintaining a constant, controlled, or variable current to high current loads like laser diodes and LEDs, while minimizing heat generation and capacitance requirements.
Implementation Method 1
an inductor L, a load R and a diode D... In FIG. 6A, the switch S is closed, and current flows through the inductor L and through the load R... In FIG. 6B, the switch S is opened, and current continues to flow through the inductor L, through the load R, and through the diode D
Implementation Method 2
The diode D is connected as a flyback, or freewheeling diode, via the load R, across the inductor L... current continues to flow through the inductor L, through the load R, and through the diode D
Data Source
AI summary
A current-driven load such as LEDs or laser diodes is driven by a current driver having a two stages (or phases), the outputs of which have ripple which is forced to be out-of-phase with one another. In analog embodiments, an output (ripple or switching) of a master stage hysteresis controller is phase-shifted and scaled, and modulates the input of a slave stage hysteresis controller so that the slave stage pulls into a ripple-canceling phase. In digital embodiments, a faster of the two phases is designated “master”, maximum and minimum thresholds are set, and the slave phase's on time is based on a previous cycle's slave phase ON time, the master stage OFF time and an offset. The slave controller may “lock” to the anti-phase of the master stage (or phase). The ripple currents at the summed output of the master and slave stages substantially cancel.