Electrochromic Mirror SMPS Circuit Power Loss Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electrochromic rearview mirror assemblies suffer from inefficient power management, leading to significant power losses due to the use of linear regulators and inefficient transistor operation, which results in increased power dissipation and reduced efficiency in controlling the reflectance of the mirror reflective element.
Innovation Solution
A switch mode power supply (SMPS) electrochromic driving circuit with a fixed voltage switching regulator, a MOSFET drive transistor, a bipolar junction transistor for bleaching, and a controller for precise voltage control, minimizing power losses and allowing for efficient dimming of the electrochromic cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If linear regulators are used to provide voltage to the electrochromic cell, then the circuit is simple to implement, but power losses are significant
Solution Approach 1:
The patent replaces linear regulators with a switching regulator that uses pulse-width modulation (PWM) to control power delivery to the electrochromic cell. This substitution changes the fundamental mechanism from continuous linear voltage regulation to switched-mode PWM control, achieving greater than 50% power efficiency while maintaining circuit functionality.
2Device complexity
If conventional transistor operation is used to control the electrochromic cell, then the control circuit is simple, but power dissipation is increased
Solution Approach 1:
The patent employs pulse-width modulation (PWM) where the transistor switches on and off periodically at high frequency. By varying the duty cycle of these periodic pulses, the average power delivered to the electrochromic cell is precisely controlled while minimizing resistive power dissipation in the transistor, achieving efficient power control.
Solution Approach 2:
The control system dynamically adjusts the PWM duty cycle in real-time based on ambient light conditions and desired mirror reflectance. This dynamic control allows the transistor to operate in switching mode rather than linear mode, significantly reducing power dissipation while maintaining precise control capability.
3Speed
If higher power is delivered to the electrochromic cell for faster response, then the dimming speed increases, but power consumption increases
Solution Approach 1:
The PWM switching regime delivers power in periodic pulses rather than continuous flow. By adjusting the duty cycle, the system can deliver high peak power for rapid electrochromic response while the average power consumption remains low due to the pulsed nature of delivery, resolving the contradiction between speed and power consumption.
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 SMPS circuit achieves greater than 50% efficiency, reducing power draw and temperature, enabling precise dimming control and fault detection, while minimizing PCB area and standby current consumption.
Implementation Method 1
The mirror reflective element may comprise a variable reflectance mirror reflective element that varies its reflectance responsive to electrical current applied to conductive coatings or layers of the reflective element
Data Source
AI summary
A vehicular electrochromic rearview mirror assembly includes a base for attaching at a vehicle, a mirror casing at the base, and a mirror reflective element sub-assembly at the mirror casing and including an electrochromic (EC) cell and an EC driving circuit. The EC driving circuit includes a fixed voltage switching regulator for providing voltage to a power input of the EC cell, a drive transistor connected to an output of the fixed voltage switching regulator for switching the provided voltage on and off, a protection diode connected to the drive transistor and the EC cell, a bleach transistor connected to the power input of the EC cell and to ground, and a controller connected to the fixed voltage switching regulator, the drive transistor, and the bleach transistor. The controller controls the fixed voltage switching regulator, the drive transistor, and the bleach transistor to control the voltage provided to the EC cell.