Thermal Switch Circuit Resolving Power Loss and Rush Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric circuits face issues with power loss, high cost, large size, and limited reusability in protecting components from rush currents and abnormal heat generation, particularly with current limiting resistors and thermal fuses.
Innovation Solution
An electric circuit with a thermal switch having three terminals, comprising a fixed conductor, a movable plate with elastic contact, and a bimetal element that closes at specified temperatures, allowing for low power loss, general-purpose, low-cost, and repeated use in various circuits, including those with lightning arrestors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current limiting resistor is used to limit rush current, then the component is protected from excessive current, but power loss increases due to fixed resistance
Solution Approach 1:
The patent uses a thermistor whose resistance changes with temperature. At room temperature, the thermistor has high resistance to limit rush current. After heating from the rush current, the resistance drops to maintain low power loss during normal operation. This dynamic parameter change resolves the contradiction between protection and power loss.
Solution Approach 2:
The patent introduces a bimetallic switch that dynamically changes the circuit configuration based on temperature. When the thermistor heats up, the bimetallic switch opens to disconnect the current limiting resistor, transitioning the system from a high-resistance protection state to a low-resistance normal operation state, thereby reducing power loss.
2Reliability
If a power thermistor is used for current limiting, then rush current is limited, but the current limiting effect is insufficient during hot start state
Solution Approach 1:
The patent incorporates a bimetallic switch that anticipates the hot start problem. After the power supply is turned off, the bimetallic switch remains open for a predetermined time to prevent immediate re-energization. This preliminary action ensures the thermistor has sufficient time to cool down, guaranteeing effective current limiting on the next startup without waiting for natural cooling.
3Reliability
If a relay is used to short-circuit the current limiting resistor, then component damage is prevented, but power loss occurs in driving the relay
Solution Approach 1:
The patent replaces the electromagnetic relay with a bimetallic thermal switch. The bimetallic switch uses thermal expansion and contraction of bimetallic strips to open or close the circuit, eliminating the need for continuous electrical power to maintain the switched state. This mechanical/thermal actuation system consumes no power during operation, only requiring minimal power for the thermistor's heating function.
4Reliability
If a thermal fuse is used to protect against abnormal heat, then component protection is achieved, but the device cannot be reused
Solution Approach 1:
The patent employs a bimetallic switch that dynamically responds to temperature changes. When abnormal heat is detected, the bimetallic strip bends to open the circuit, protecting the components. Once the temperature returns to normal, the bimetallic strip automatically returns to its original position and closes the circuit, enabling the device to be reused without replacement, unlike a thermal fuse.
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 thermal switch effectively limits rush currents and prevents damage by quickly activating and deactivating to manage heat, reducing power loss and enabling efficient reuse while maintaining current limiting functionality.
Implementation Method 1
a bimetal element (5) engaged with the movable plate (4) and opened and closed at a specified temperature
Implementation Method 2
a movable plate (4) formed by an elastic substance provided with a movable contact (13)
Implementation Method 3
The thermal switch effectively limits rush currents and prevents damage by quickly activating and deactivating to manage heat
Data Source
AI summary
An electric circuit connected to a thermal switch with three terminals and a method for connecting the switch are realized. In an electric circuit of a common power supply, an external connection wire (first terminal) of a thermal switch arranged close to a current limiting resistor is connected to a load side (rectifier circuit), the current limiting resistor is connected between the external connection wire (first terminal) and an external connection wire (second terminal), and an external connection wire (third terminal) is connected to the output side of a power supply switch. Thus, the current limiting resistor is connected and arranged to an internal resistor unit of the thermal switch in series and to a switch unit (contact) in parallel.