PWM Laser Diode Drive Circuit Reduces Heat
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Solution Overview
Problem
Battery-powered laser devices face challenges with high heat dissipation and component costs due to analog linear control systems, which are complex and unreliable, limiting the efficient delivery of energy to the laser.
Innovation Solution
Implementing a digital pulse width modulation (PWM) control system reduces the number of components, minimizes heat on the circuit board, and increases energy delivery to the laser by generating heat at the battery, thereby reducing costs and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an analog linear control system is used to drive the laser diode, then the laser can be powered continuously, but significant heat is dissipated on the circuit board and the system complexity increases
Solution Approach 1:
The patent applies periodic pulsed action by switching the laser diode on and off at high frequency using PWM control. Instead of continuous analog control, the system delivers energy in periodic pulses, which reduces average power dissipation on the circuit board while maintaining effective laser operation. This transforms the continuous control problem into a periodic switching problem, simplifying the control system architecture.
Solution Approach 2:
The patent replaces the analog linear control system (mechanical/electrical continuous control) with a digital PWM control system. This substitution transitions from continuous analog voltage control to digital pulse width modulation, reducing component count and system complexity while achieving the same energy delivery function through digital switching control.
2Use of energy by moving object
If an analog linear control system is used to drive the laser diode, then the laser can be powered continuously, but the bill of materials cost increases due to multiple components
Solution Approach 1:
The patent extracts and removes unnecessary components from the control system by replacing the analog linear control architecture with digital PWM control. This extraction eliminates op-amps, analog voltage regulators, and associated precision components, reducing the bill of materials cost while maintaining the essential function of delivering energy to the laser diode.
Solution Approach 2:
The patent employs inexpensive digital switching components (MOSFETs, microcontroller PWM outputs) instead of expensive analog control components. The digital switching elements are simpler, more reliable, and significantly cheaper than the analog op-amps and precision resistors required for linear control, reducing overall manufacturing cost.
3Use of energy by moving object
If an analog linear control system is used to drive the laser diode, then the laser can be powered continuously, but reliability decreases due to heat generation
Solution Approach 1:
By using periodic pulsed operation instead of continuous analog control, the system reduces average heat generation on the circuit board. The laser diode receives full power during pulse intervals but the overall average power dissipation is reduced, improving component reliability and reducing thermal stress on the system.
Solution Approach 2:
The patent converts the potentially harmful heat dissipation issue into a benefit by using PWM control. The switching action concentrates power delivery into brief intervals, allowing the circuit board and components to cool between pulses. This transforms the heat management problem into an advantage where thermal cycles improve reliability rather than degrade it.
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 PWM control system enhances energy efficiency, reduces heat dissipation on the circuit board, and lowers the bill of materials cost, while maintaining or improving the delivery of energy to the laser, thus addressing the limitations of analog linear control systems.
Implementation Method 1
a microcontroller programmed to pulse width modulation (PWM) control to switch on and off the control FET Q2 at a high frequency, e.g., 20-100 kHz
Implementation Method 2
The high power dissipation of the control FET generates heat on the circuit board, which may negatively affect other parts of the circuit
Data Source
AI summary
A battery-powered laser-based dermatological treatment device may include a laser unit comprising at least one laser diode, a battery unit, at least one sensor configured to generate sensor signals, and a laser drive control system including a laser drive circuit comprising the laser unit, the battery unit, a first switch (e.g., a first FET), and a second switch (e.g., a second FET), wherein the laser unit is arranged in series between the first switch and the second switch, and control electronics configured to control the first switch based at least on sensor signals from the at least one sensor, and control the second switch using pulse width modulation (PWM), thereby delivering current from the battery unit to the laser unit with a PWM current waveform. The laser drive circuit may also include a snubber circuit configured to prevent voltage spikes upon the second switch being turned off.