SMPS Thermal Protection Circuit With Temperature-Based Timer Limits
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Solution Overview
Problem
Switch mode power supplies lack effective thermal protection for semi-conductors, leading to potential thermal damage and premature failure, especially when operating at low input voltages and high current demands, and existing solutions like over-sizing components or using smart MOSFETs are costly or inefficient.
Innovation Solution
A thermal protection circuit that includes an ambient temperature sensor to adjust the maximum time transistors can conduct current based on temperature, using a counter and comparator to prevent overheating by shutting off the transistors when the maximum time is reached.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the maximum count is fixed regardless of temperature, then the control logic is simple, but the semi-conductors may be damaged at high temperatures where shorter operation time is needed
Solution Approach 1:
The maximum count is made dynamic by adjusting it according to the detected temperature. At higher temperatures, the maximum count is reduced to limit operation time and prevent thermal damage. At lower temperatures, the maximum count is increased to allow longer operation. This dynamic adjustment resolves the contradiction by adapting the protection level to actual thermal conditions.
Solution Approach 2:
A temperature sensor provides feedback about the actual temperature to the control circuit, which then adjusts the maximum count accordingly. This closed-loop feedback mechanism enables the system to automatically adapt the operation time limit based on thermal conditions, improving reliability without requiring manual intervention or overly complex predetermined tables.
2Reliability
If a fixed maximum operation time is used, then the timer control is simple, but it does not account for temperature-dependent thermal damage risks
Solution Approach 1:
The timer's maximum count is dynamically adjusted based on temperature readings. Rather than using a single fixed time limit, the system calculates an appropriate maximum operation time based on the detected temperature, allowing longer operation in cool conditions and shorter operation in hot conditions to prevent thermal damage.
Solution Approach 2:
The time parameter of the timer is changed based on temperature. The system monitors temperature and adjusts the maximum operation time parameter accordingly, transforming a static timing control into a temperature-dependent dynamic control that accurately reflects thermal damage risks at different operating conditions.
3Productivity
If the maximum count is increased to allow longer operation, then productivity is improved, but the semi-conductors may overheat and fail
Solution Approach 1:
The system dynamically adjusts the maximum operation time based on real-time temperature monitoring. When temperatures are low, the maximum count is increased to allow longer operation and improve productivity. When temperatures rise, the maximum count is reduced to prevent overheating and failure. This dynamic adaptation resolves the contradiction between maximizing productivity and preventing thermal damage.
Solution Approach 2:
The system periodically monitors temperature and adjusts the maximum operation count accordingly. This periodic checking and adjustment allows the system to maximize operation time during safe temperature periods while preventing overheating when temperatures rise, effectively managing the trade-off between productivity and thermal safety.
4Reliability
If over-sized power components are used, then thermal protection is provided, but the size and cost of the power supply increases
Solution Approach 1:
The system takes preliminary action by monitoring temperature and limiting operation time before thermal damage can occur. By proactively controlling the duty cycle based on temperature and accumulated operation time, the system prevents overheating without requiring oversized components with excessive thermal mass or surface area for heat dissipation.
Solution Approach 2:
The patent replaces the mechanical/physical solution of using oversized heat sinks and large power components with an electronic control solution. Instead of relying on passive thermal management through larger physical components, the system uses active electronic control of the duty cycle and operation time based on temperature feedback, achieving thermal protection with compact components.
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
Extends the operational time of semi-conductors before thermal damage by dynamically adjusting the current flow duration based on ambient temperature, preventing premature failure and reducing component size and cost.
Implementation Method 1
A thermal protection circuit for a switch mode power supply includes an ambient temperature sensor
Data Source
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AI summary
The maximum time that external components of a switch mode power supply overconduct is determined by an actual ambient temperature at which the devices are operating before they are turned on. Their operation time is thus extended when temperatures are low and decreased when temperatures are high.