Freewheeling Circuit Switching Threshold for Inductive Load Overvoltage
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Solution Overview
Problem
Inductive loads, such as coil contactor switches, experience slow dissipation of magnetic energy when the control supply voltage is removed, leading to potential welding of contacts and reduced service life due to high power losses and two-stage drop issues in existing freewheeling circuits.
Innovation Solution
Incorporating an ohmic resistance component and a switching threshold component in the freewheeling circuit, allowing for earlier activation of the freewheeling circuit by setting a switching threshold, which reduces turn-off overvoltage and eliminates two-stage drops without the need for electronic coil control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a diode or zener diode is used in the freewheeling circuit, then the magnetic energy can be dissipated, but high power losses occur constantly
Solution Approach 1:
The patent applies dynamics by making the freewheeling circuit switchable rather than permanently active. The circuit is activated only when needed (during turn-off transients) and deactivated during normal operation, transforming a static energy-dissipating structure into a dynamic one that adapts its state based on operational requirements, thereby eliminating constant power losses while maintaining energy dissipation capability when required
2Loss of energy
If the freewheeling circuit is switched on and off controlled, then power losses are reduced, but the freewheeling circuit activates too late when control supply voltage fails
Solution Approach 1:
The patent replaces the electronic control system (coil control electronics with switching thresholds) with a direct voltage-based activation mechanism. The freewheeling circuit activates automatically when the control supply voltage drops below a certain level, eliminating the delay inherent in electronic evaluation and switching processes. This substitution of control mechanism enables immediate response to voltage failures while maintaining the ability to reduce power losses during normal operation
3Ease of operation
If coil control electronics are used to switch the freewheeling circuit, then the circuit can be controlled, but complex electronic control is required and components increase
Solution Approach 1:
The patent extracts and removes the complex coil control electronics from the system, retaining only the essential freewheeling circuit components (diode, resistor, capacitor). By eliminating the electronic control layer with its switching thresholds and evaluation logic, the solution achieves controlled switching through a simpler voltage-based mechanism, thereby reducing device complexity and component count while maintaining operational control
4Stability of the object's composition
If the control supply voltage must be almost completely dissipated before freewheeling activates, then the capacitive energy store can be discharged, but the activation is delayed and two-stage drop occurs
Solution Approach 1:
The patent applies preliminary anti-action by preparing the freewheeling circuit for immediate activation through a capacitor that is pre-charged during normal operation. When the control supply voltage fails, this pre-charged capacitor provides the necessary voltage to immediately activate the freewheeling diode, counteracting the delay that would otherwise occur while waiting for complete voltage dissipation. This preliminary preparation eliminates the two-stage drop by ensuring continuous protective action
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 enables quicker dissipation of energy, prevents contact welding, extends contact life, and reduces component count, while ensuring the freewheeling circuit activates earlier and reduces turn-off overvoltage, even when the control supply voltage is switched off or fails.
Implementation Method 1
an existing capacitive energy storage device is discharged
Implementation Method 2
a voltage-dependent resistor 7, which reduces the turn-off overvoltage
Implementation Method 3
the magnetic energy stored in the inductive load is dissipated
Data Source
Figure 1
AI summary
The invention relates to a free-wheeling circuit for the rapid reduction of a shutdown overvoltage of an inductive load (1) when the latter is shut down. The free-wheeling circuit comprises a switching threshold component (11) by which the free-wheeling circuit becomes active more rapidly compared to a free-wheeling circuit without said switching threshold component (11), thereby ensuring a more rapid reduction of the shutdown overvoltage. If a control voltage provided by a control voltage source (2) falls below a threshold voltage set by the switching threshold component (11), a capacitive energy accumulator is immediately discharged and not only when the control voltage is reduced to near zero, and said energy accumulator then activates the free-wheeling circuit for reducing the shutdown overvoltage, when in the nearly discharged state.