Over-temperature Protection Circuit for DC Electric Tools
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Solution Overview
Problem
Existing over-temperature protection circuits for DC electric tools face challenges in accurately monitoring the core temperature of power devices due to thermal lag caused by heat transfer delays and poor thermal conductivity, leading to potential overheating failures.
Innovation Solution
An over-temperature protection circuit that includes a current detecting circuit, a power device control circuit, and a computation control circuit using MCU software to predict overheating and shut down the power device quickly, utilizing existing current sampling circuits without additional hardware costs, and combining with conventional temperature and overcurrent protection methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external temperature measurement element is mounted on the power device to monitor temperature in real time, then the temperature can be monitored, but the measured temperature lags behind the actual core temperature due to heat transfer delays and poor thermal conductivity
Solution Approach 1:
The patent replaces the mechanical/physical temperature measurement system (external temperature measurement element mounted on power device) with an electrical calculation system. The microcontrol unit calculates core temperature based on voltage and current measurements, bypassing the thermal conduction path entirely. This substitution eliminates the time lag caused by heat transfer while maintaining temperature monitoring capability.
Solution Approach 2:
The patent introduces voltage and current measurements as intermediary parameters to infer core temperature. Instead of directly measuring temperature (which suffers from thermal lag), the system measures electrical parameters (voltage and current) that can be instantly obtained and used to calculate temperature, serving as intermediaries between the power device operation and temperature assessment.
2Temperature
If thermal conductive material is filled in the air gap between temperature measurement element and power device to improve thermal conductivity, then thermal contact is improved, but the time lag phenomenon still exists and manufacturing complexity increases
Solution Approach 1:
The patent replaces the thermal conduction-based temperature measurement approach (requiring thermal conductive material and precise mechanical installation) with an electrical measurement and calculation approach. This eliminates the need for thermal conductive materials and complex installation procedures while achieving accurate core temperature monitoring without time lag.
3Measurement precision
If the temperature measurement element is mounted on the heatsink of the power device, then the measured temperature is closer to the core temperature, but electrical isolation requirements reduce thermal conductivity and increase measurement lag
Solution Approach 1:
The patent replaces the thermal conduction path (which requires physical mounting on heatsink and suffers from electrical isolation constraints) with an electrical calculation method. The microcontrol unit calculates core temperature from voltage and current measurements, eliminating the need for thermal contact and avoiding the thermal conductivity reduction caused by electrical isolation requirements.
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
Effectively prevents overheating failures by accurately predicting temperature changes and shutting down the power device in a timely manner, enhancing the tool's operational safety and extending its lifespan.
Implementation Method 1
a current detecting circuit electrically connecting to a battery pack and detecting the current in the circuit
Implementation Method 2
a computation control circuit for controlling the power supply of the motor according to the current value detected by the current detecting circuit
Data Source
AI summary
An over-temperature protection circuit for a direct current (DC) electric tool includes a current detecting circuit electrically coupled to a battery pack, a power device control circuit electrically coupled to an electric motor of the DC electric tool and a power device for controlling the power state of the circuit. A computation control circuit controls the power supply of the motor according to the circuit current value detected by the current detecting circuit. When the electric motor is not in a speed control state, the allowable current passing through the over-temperature protection circuit of the DC electric tool cannot exceed a preset first current value. When the electric motor is in the speed control state, the allowable current passing through the over-temperature protection circuit of the DC electric tool cannot exceed a preset second current value less than the first current value.