PWM Heater Control for MEMS Temperature and Power Limits

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Solution Overview

Problem

MEMS devices in sensor block assemblies face challenges in maintaining temperature within a predefined threshold due to limited power and current constraints, especially under varying voltage conditions, which can lead to excessive power draw and current limits.

Innovation Solution

A pulse width modulation (PWM) control system with a power limiter and current limiter is implemented, adjusting the duty factor of a switch to manage power and current drawn by a resistive load, adhering to specified limits by using a slope-intercept curve to modify the duty factor and limit power and current accordingly.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the duty factor is increased to maintain constant delivered power when power supply voltage decreases, then the delivered power is maintained, but the input current increases and may exceed the specified RMS current limit

Engineering Contradiction:

Improvedelivered powerVSAvoidinput current

Core Design Contradiction:

PowerVSUse of energy by moving object

Solution Approach 1:

The system dynamically adjusts the duty factor based on real-time voltage conditions and power requirements. When voltage decreases, the duty factor is increased to maintain power, but this is done dynamically rather than statically, allowing the system to respond to changing conditions and prevent current limits from being exceeded through continuous monitoring and adjustment.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the duty factor parameter in response to voltage changes to maintain constant delivered power. This parameter adjustment is the core mechanism for resolving the contradiction between maintaining power output and limiting input current under varying voltage conditions.

Inventive Principle:

Principle #35Parameter changes

2Temperature

If the heater operates at high power to maintain MEMS device temperature, then temperature control is effective, but the power draw may exceed the specified power budget

Engineering Contradiction:

ImproveMEMS device temperatureVSAvoidpower draw

Core Design Contradiction:

TemperatureVSUse of energy by stationary object

Solution Approach 1:

The system uses feedback from temperature sensing to regulate heater operation. When the MEMS device temperature approaches the desired threshold, the feedback signal reduces the duty factor, thereby reducing power draw. This closed-loop control ensures effective temperature maintenance while preventing power budget violations.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The PWM controller applies periodic switching action to the heater, turning it on and off in controlled cycles. This periodic action allows the heater to deliver effective heating during on-periods while remaining off during off-periods, thereby maintaining temperature control within the power budget through duty cycle management.

Inventive Principle:

Principle #19Periodic action

3Adaptability or versatility

If the system operates independently of power source voltage to ensure reliable temperature control, then adaptability is improved, but the control system complexity increases due to voltage compensation requirements

Engineering Contradiction:

Improvevoltage independenceVSAvoidcontrol system complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The system replaces complex mechanical voltage regulation mechanisms with electronic PWM control. By using electronic switching and duty factor adjustment, the system achieves voltage independence through software/control logic rather than complex hardware, thereby reducing overall system complexity while maintaining adaptability to varying voltage conditions.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 effectively maintains temperature control within MEMS devices by closely adhering to power and current limits, independent of power source voltage, ensuring efficient operation within defined budgets and preventing excessive power or current draw.

Implementation Method 1

Since a heater is typically a resistive device, the generated heat will decrease as the power supply voltage decreases

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

a pulse width modulation (PWM) controller may increase the duty factor, and thus increase input current, to maintain a constant delivered power

Methodology Applied

Scientific EffectPulse width modulation:

Data Source

PatentUS8324538B2Systems and methods for limiting input power and RMS input current drawn from a DC power source

Publication Date: 2012.12.04 HONEYWELL INTERNATIONAL INC

AI summary

Systems and methods to source a resistive load, such as a heating resistor, to control temperature while adhering to a specified power draw budget and/or a specified root mean square (RMS) current limit. For example, a sensor block assembly (SBA) heater controls temperature of a MEMS device in a sensor block assembly while adhering to the power draw budget and/or an average current limit. An exemplary embodiment generates a pulse width modulation (PWM) control signal, controls a switch in accordance with the control signal, sources the resistive load from a power source in accordance with the controlled switch, and modifies the duty factor of the switch to reduce the power drawn by the resistive load in response to the power drawn by the resistive load exceeding a power limit defined by a slope-intercept curve. The limiting of power into a resistor load limits the RMS current drawn by that load.