Inductive Clamping Circuit for MOSFET Junction Temperature Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In inductive load switching, existing control methods fail to accurately time the zero crossing, leading to residual energy dissipation in semiconductor switches, causing excessive heating and potential damage due to inefficient energy absorption in solid state power controllers.
Innovation Solution
A method involving a solid state power controller with two sequentially arranged switching devices and diodes, where one device is switched off before the zero crossing and the other is delayed and then switched off after, allowing the body diode to act as a free-wheeling diode to dissipate energy in the wiring and load, reducing heat in the semiconductor switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the inductive load is switched off at a point other than zero crossing, then the switching can occur at any desired time, but significant energy is stored in the inductive load and dissipated within the MOSFETs causing junction temperatures to rise rapidly
Solution Approach 1:
A clamping circuit comprising a clamping diode and a capacitor is introduced as an intermediary between the inductive load and the MOSFETs. The clamping diode provides a dedicated path for flux current to flow into the capacitor, preventing this current from flowing through the MOSFETs. This mediator absorbs the harmful flux energy and redirects it safely, resolving the contradiction by enabling flexible switching timing while maintaining safe operating temperatures.
Solution Approach 2:
The harmful flux current path is extracted from the MOSFETs by introducing the clamping diode and capacitor combination. The flux current is diverted through the clamping diode into the capacitor, separating the energy dissipation function from the switching device. This extraction allows the MOSFETs to perform their switching function without bearing the thermal burden of flux energy dissipation.
2Measurement precision
If existing control methods are used to track zero crossing, then switching can be timed to occur near zero crossing, but control errors result in residual energy remaining in the inductive load that must still be dissipated by the semiconductor switches
Solution Approach 1:
The invention converts the previously harmful flux energy that needed to be dissipated by the MOSFETs into a beneficial charging current for the capacitor. The clamping diode guides the flux current to charge the capacitor, transforming what was a harmful thermal effect into a useful energy storage function. This resolves the contradiction by ensuring that even with control errors, the residual energy is harmlessly stored in the capacitor rather than damaging the semiconductor switches.
3Device complexity
If mechanical switches and toggles are used, then the switching operation is simple, but the majority of energy is dissipated in arcing at the switch or toggle
Solution Approach 1:
The invention replaces the mechanical switching system with a solid state power controller using MOSFETs, eliminating the arcing problem inherent in mechanical contacts. The MOSFETs provide clean, contactless switching while the clamping circuit manages the flux energy. This substitution resolves the contradiction by achieving simple operation through solid state devices without the energy-wasting arcing characteristic of mechanical switches.
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 approach minimizes energy dissipation in semiconductor switches, reducing junction temperatures and preventing damage by aligning diodes with AC current polarity and timing switch-offs to avoid peak energy absorption during zero crossings.
Implementation Method 1
allowing the body diode to act as a free-wheeling diode to dissipate energy in the wiring and load, reducing heat in the semiconductor switches
Implementation Method 2
An inductive load creates a phase lag on current and stores energy in the inductive flux at the load
Data Source
AI summary
A power control circuit includes a solid state power controller operable to connect an AC power source to a load. The solid state power controller includes a first switching device and a second switching device arranged serially. Each of the switching devices includes a diode, a controller controllably coupled to each of the first switching device and the second switching device, such that the controller is capable of controlling an on/off state of the first switching device and the second switching device. The controller further includes a non-transitory memory storing instructions for causing the controller to perform the steps of: switching off a first switching device having a diode aligned with a current polarity of an AC current flow prior to a first zero crossing, delaying a switching off of a second switching device until after the first zero crossing, and switching the second switching device off after the delay and before a second zero crossing.