Pulsed Laser Diode Drive Circuit Without Charging Resistor Heat
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Solution Overview
Problem
Current control circuits for LiDAR-based environmental sensors in vehicles experience heat-related issues due to charging series resistors, leading to inefficient laser diode operation and increased cooling requirements, as well as potential uncontrolled light emission from the laser diode if the switch fails.
Innovation Solution
A switched-mode power supply unit with a primary and secondary circuit, including a storage capacitor and a second switch in parallel, allows for pulsed charging and discharging of the capacitor without a charging series resistor, reducing heat generation and providing decoupling between the supply voltage and the light-emitting means, thus minimizing losses and improving electromagnetic compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a charging series resistor is used to charge the storage capacitor, then the capacitor can be charged continuously, but heat is generated at the resistor which heats the laser diode and causes wavelength shifts and efficiency degradation
Solution Approach 1:
The patent applies periodic action by charging the storage capacitor in discrete charge pulses instead of continuous charging. The control unit activates the first switch periodically to generate charge pulses that charge the capacitor in steps, rather than maintaining continuous current flow through a series resistor. This periodic charging approach eliminates continuous heat generation at the resistor while still achieving the required capacitor charge level before laser pulse emission.
Solution Approach 2:
The patent extracts and removes the charging series resistor from the circuit. By eliminating this component entirely and replacing it with a switched-mode power supply using a first switch, the source of heat generation is removed. The capacitor is charged directly through the switch without any series resistance, thereby eliminating the heat that would otherwise transfer to the laser diode and cause wavelength shifts and efficiency degradation.
2Reliability
If the switch is defective and remains closed, then the laser diode may permanently emit light, but this creates safety hazards as uncontrolled emission is not eye-safe
Solution Approach 1:
The patent introduces an intermediary element - the storage capacitor - between the switch and the laser diode. The capacitor acts as a buffer that stores energy and controls its release. Even if the first switch fails and remains closed, the capacitor can still be discharged through the second switch which is controlled by the control unit. This intermediary capacitor provides an additional control layer that prevents uncontrolled light emission and maintains eye safety.
Solution Approach 2:
The patent implements beforehand cushioning by using the storage capacitor to buffer and control energy delivery to the laser diode. The capacitor is charged in advance through pulsed charging, and its discharge is precisely controlled by the second switch. This pre-charging mechanism with controlled discharge acts as a safety cushion, ensuring that even in switch failure scenarios, the laser diode cannot emit light uncontrollably, thereby maintaining eye safety.
3Power
If a step-up converter is used to generate high voltage from vehicle electrical system, then the required pulse drive voltage can be achieved, but the laser diode is not decoupled from the vehicle electrical system and electromagnetic interference occurs
Solution Approach 1:
The patent uses the storage capacitor as an intermediary element that decouples the laser diode from the vehicle electrical system. The capacitor is charged from the vehicle electrical system through the switched-mode power supply, but once charged, it provides isolated energy to the laser diode. This intermediary capacitor breaks the direct electrical connection, preventing electromagnetic interference and noise propagation between the vehicle electrical system and the laser diode while still enabling high voltage pulse drive.
Solution Approach 2:
The patent segments the electrical system into distinct functional blocks: the vehicle electrical system, the switched-mode power supply with first switch, the storage capacitor, and the laser diode drive circuit with second switch. This segmentation isolates the laser diode operation from the vehicle electrical system, allowing independent control and reducing electromagnetic interference. The charge pulses segment the energy transfer into discrete events rather than continuous connection.
4Temperature
If additional cooling devices are added to prevent laser diode heating, then the temperature can be controlled, but the construction size increases and space is consumed
Solution Approach 1:
The patent converts the potential harm of heat generation into a benefit by eliminating the source of heat (charging series resistor) and using the switched-mode power supply with pulsed charging. This approach not only prevents overheating but also improves overall system efficiency. By removing the harmful heat-generating component and using efficient pulsed charging, the system achieves temperature control without requiring additional cooling devices, thus avoiding increased construction size.
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 solution reduces heat generation and wavelength shifts in the laser diode, enhances efficiency, and eliminates the need for additional cooling, while ensuring safe operation and improved electromagnetic compatibility by using charge pulses to target capacitor charging and minimizing alternating current loads.
Implementation Method 1
A storage capacitor (68) arranged between the secondary-side connector (67) and a ground (66)
Implementation Method 2
control unit (72) to control the first and the second switch (64, 70), wherein the control unit is designed to operate the first switch (64) to induce at least one charge pulse for charging the storage capacitor (68)
Implementation Method 3
generate a light pulse via the light-emitting means (52)
Implementation Method 4
A transformer (56) with a primary coil (58) arranged on a primary side (59) of the switched-mode power supply unit (54) and a secondary coil (60) arranged on a secondary side (61) of the switched-mode power supply unit (54)
Data Source
AI summary
The invention relates to a control circuit (50) for pulsed control of a light-emitting means (52), in particular an LED or a laser diode (52), having a switched-mode power supply unit (54) with a first switch (64) arranged in a primary circuit of the switched-mode power supply unit (54), wherein the switched-mode power supply unit (54) has a primary-side connector (62) for connection to a supply voltage, a secondary-side connector (67) for supplying the light-emitting means (52) and a switching input (65) for operating the first switch (64), having a storage capacitor (68) arranged between the secondary-side connector (67) and a ground (66), having a second switch (70) arranged in a current path (71) in parallel with the storage capacitor (68), wherein the light-emitting means (52) is positionable in the current path (71), and having a control unit (72) to control the first and the second switch (64, 70), wherein the control unit (72) is designed to operate the first switch (64) in order to induce at least one charge pulse for charging the storage capacitor (68) in the secondary circuit and to operate the second switch (70) in order to discharge the storage capacitor (68) while generating a light pulse (82) via the light-emitting means (52). The invention also relates to a LiDAR-based environmental sensor, in particular a laser scanner, for use in a vehicle, having an abovementioned control circuit (50) and a laser diode (52). The invention further relates to a method for the pulsed control of a light-emitting means (52), in particular an LED or a laser diode (52), comprising the steps of providing a storage capacitor (68) and a current path (71) that is parallel thereto and in which the light-emitting means (52) is arranged, of generating at least one charge pulse for charging the storage capacitor (68), and of discharging the storage capacitor (68) via the light-emitting means (52) while generating a light pulse (82).