DC/DC Converter Temperature Control for Low-Mass Resistive Heaters
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Solution Overview
Problem
Heated aerosol-generating devices face challenges in controlling the temperature of resistive heating elements, particularly when using pulse width modulation (PWM), which can lead to overheating and inefficiency due to limitations in design flexibility and battery voltage constraints, especially with low-mass heaters and varying substrate conditions.
Innovation Solution
A control unit incorporating a DC/DC converter and a microcontroller that adjusts the output voltage based on a predetermined temperature profile for the resistive heater, allowing for more precise and flexible temperature control, including the use of closed-loop and open-loop control schemes, and the ability to monitor and manage current and voltage to prevent overheating and ensure battery voltage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pulse width modulation (PWM) is used to control the heating element temperature, then simple and highly reactive control is achieved, but the heating element may overheat during ON periods especially when the heater mass is low
Solution Approach 1:
A low-pass filter circuit is introduced as an intermediary between the PWM signal generator and the heating element. This filter converts the pulsed PWM signal into a smoothed voltage signal, preventing temperature spikes while maintaining control simplicity. The filter acts as a mediator that transforms the harsh PWM waveform into a gentler control signal suitable for low-mass heaters.
Solution Approach 2:
The invention changes the control parameter from direct PWM duty cycle control to filtered voltage control. By adjusting the cutoff frequency of the low-pass filter and the PWM frequency, the system optimizes the balance between response time and temperature stability, allowing effective control of low-mass heaters without overheating.
2Temperature
If PWM frequency is increased to reduce temperature spikes, then temperature control improves, but device efficiency drops
Solution Approach 1:
The system optimizes the PWM frequency parameter to a specific range that balances temperature control precision with energy efficiency. The low-pass filter allows moderate PWM frequencies to be used effectively, avoiding the high frequencies that would waste energy while still achieving smooth temperature control. The filter cutoff frequency is tuned to work synergistically with the PWM frequency.
3Temperature
If heater structure mass is increased to reduce temperature spikes, then temperature stability improves, but heating time increases
Solution Approach 1:
The low-pass filter serves as an intermediary that provides thermal control stability without requiring increased heater mass. The filter smooths the electrical input signal, which in turn stabilizes the thermal output, allowing low-mass heaters to achieve temperature stability that would otherwise require significant thermal mass.
Solution Approach 2:
The invention replaces the mechanical approach of increasing heater mass to achieve temperature stability with an electrical approach using signal filtering. Instead of adding physical thermal mass, the system uses electronic filtering to achieve the same stabilizing effect, thereby maintaining fast heating response.
4Adaptability or versatility
If PWM control is used with low-mass heaters, then design flexibility is maintained, but overheating risk increases
Solution Approach 1:
The low-pass filter is a universal intermediary component that can be applied to various heater designs without changing the fundamental heater structure. It maintains design flexibility by working with different heater types while providing reliable overheating protection through signal smoothing, regardless of the specific heater configuration.
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 provides smoother temperature control, reduces the risk of overheating, and allows for more design flexibility in heater structures, ensuring efficient and reliable aerosol production while maintaining battery health.
Implementation Method 1
a DC/DC converter arranged to receive as an input the battery voltage from the battery and to output an output voltage to the resistive heater
Implementation Method 2
an electrically resistive heating element is used to heat an aerosol-forming substrate
Implementation Method 3
A temperature sensor may be provided adjacent to the heating element for feedback to power converter. The temperature feedback can be used to maintain the heater within a target temperature range.
Data Source
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AI summary
A control unit (1) for an aerosol-generating device (2), the aerosol-generating device (2) comprising a resistive heater (3) and a battery (4), wherein the battery (4) is configured to generate a battery voltage (Vbat), wherein said control unit (1) comprises: a DC/DC converter (11) arranged to receive as input the battery voltage (Vbat) from the battery and to output an output voltage (Vheater) to the resistive heater (3); a microcontroller (12) configured to control said DC/DC converter (11) to adjust the output voltage based on a predetermined temperature profile for the resistive heater (3). Using a DC/DC converter to adjust the DC voltage applied to the resistive heater has significant advantages over using pulse width modulation (PWM) alone, particularly when the mass of the resistive heater is low.