Pulsed Laser Diode Driver Voltage Regulation
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Solution Overview
Problem
Pulsed laser diode drivers are inefficient due to high power dissipation in current control devices, requiring large power supplies and struggling with voltage regulation during pulse current draws, leading to inefficiencies and size limitations.
Innovation Solution
A pulsed laser diode driver that continuously charges a storage capacitor to a supply voltage, automatically adjusting the capacitor voltage to ensure the current control device is almost saturated at the end of the pulse, minimizing dissipation, using a digital processor to optimize the capacitor voltage based on test pulses and feedback from the load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the storage capacitor is charged to a voltage substantially higher than the laser diode voltage requirement to maintain adequate voltage during pulse discharge, then the voltage regulation and current delivery are improved, but power dissipation in the current control device increases significantly
Solution Approach 1:
The patent implements dynamic adjustment of the storage capacitor charging voltage based on real-time monitoring of capacitor voltage droop during pulse discharge. The system continuously adapts the charging voltage to the minimum level required to maintain adequate voltage during the pulse, rather than using a fixed high voltage. This dynamic approach resolves the contradiction by allowing adequate voltage regulation during pulses while minimizing excess voltage and corresponding power dissipation in the current control device.
Solution Approach 2:
The patent employs a feedback mechanism that monitors the storage capacitor voltage during pulse discharge and uses this information to adjust the charging voltage for subsequent pulses. The system measures the voltage droop characteristics and adjusts the charging voltage accordingly to ensure adequate voltage maintenance during pulses while minimizing excess voltage. This feedback loop resolves the contradiction by optimizing the charging voltage to the precise level needed for reliable operation without unnecessary power dissipation.
2Reliability
If a large power supply is used to supply the diode current directly without a storage capacitor bank, then voltage regulation over the pulse current range is improved, but the power supply size and power rating requirements increase
Solution Approach 1:
The patent segments the power delivery function into two distinct components: a storage capacitor bank that handles the high-current pulse delivery, and a smaller power supply that only needs to recharge the capacitor between pulses. This segmentation allows the power supply to be much smaller since it only needs to provide average power rather than peak power, while the capacitor bank provides the necessary current delivery capability. The voltage regulation function is maintained through coordinated control of both components.
Solution Approach 2:
The patent uses preliminary action by charging the storage capacitor bank to the required voltage level during the interpulse period before the actual pulse current draw begins. This pre-charging ensures that when the pulse occurs, the capacitor is already prepared to deliver the required current without requiring the power supply to respond instantaneously to high current demands. This approach allows a smaller power supply while maintaining reliable voltage regulation through the capacitor's stored energy.
3Reliability
If the capacitor voltage is set higher to account for voltage droop and ESR losses during discharge, then the current delivery reliability is improved, but the dissipation in the current control device increases
Solution Approach 1:
The patent implements dynamic monitoring and adjustment of the capacitor voltage during discharge to determine the actual voltage droop and ESR losses. Rather than using a fixed conservative voltage margin, the system measures the actual performance and adjusts the charging voltage to match the minimum required level. This dynamic adaptation maintains reliable current delivery while minimizing excess voltage that would cause unnecessary dissipation in the current control device.
Solution Approach 2:
The patent changes the operating parameter of capacitor charging voltage from a fixed high value to a dynamically adjusted value based on measured performance. By monitoring voltage droop and ESR effects during discharge and adjusting the charging voltage accordingly, the system optimizes the balance between ensuring adequate voltage for reliable current delivery and minimizing excess voltage that causes power dissipation in the current control device.
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 reduces power dissipation in the current control device, allowing for smaller, more efficient, and reliable pulsed laser diode drivers, with reduced power supply requirements and improved battery life, particularly suited for low duty cycle operations.
Implementation Method 1
A pulsed current source such as the Analog Modules Model 771 or 778 laser diode drivers may be used to drive a single or stack of laser or light emitting diodes. However, this can be inefficient and dissipative because a storage capacitor bank needs to be charged to a voltage substantially higher than the laser diode voltage requirement.
Implementation Method 2
A power supply charges up the storage capacitor, or multiple capacitors (bank), to a regulated voltage level between laser pulses and a current control device such as an FET (field effect transistor) is used to regulate the current, in conjunction with a current sensing device.
Implementation Method 3
A pulsed current source such as the Analog Modules Model 771 or 778 laser diode drivers may be used to drive a single or stack of laser or light emitting diodes.
Data Source
AI summary
In a pulsed laser diode driver an energy storage capacitor is continuously being charged to a supply voltage Vr. When a pulse is initiated, energy stored in the capacitor is delivered to the laser diode load. The capacitor voltage Vd at the end of a pulse is used to control Vr to ensure that Vd is maintained above a minimum voltage Vm required to ensure operation of a current control device (such as FET) just above saturation. Test pulses (such as with attenuated currents or reduced pulsewidth) may be fired to determine an initial optimum value for Vr. After a test pulse, a slightly high estimate for Vr may be used and may be iterated (incremented) down to an optimum value Vm during a firing burst. A digital processor may be used to calculate and store data to optimize the performance. Various embodiments are disclosed.