Soft Turn-Off Active Clamp Circuit for MOSFET Overvoltage Control
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Solution Overview
Problem
Existing soft turn-off active clamp protection circuits for electric vehicle systems face high failure rates and large occupied areas due to the use of high-power TVS diodes for absorbing voltage spikes during MOSFET turn-off, which are costly and unreliable at high temperatures.
Innovation Solution
A soft turn-off active clamp protection circuit comprising a MOSFET, a discharge capacitor, an overvoltage signal acquisition module, a negative feedback module, a discharge current control module, and a turn-off control module, which forms a closed-loop negative feedback regulation system to control the turn-off speed of the MOSFET and absorb transient energy without high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-power TVS diode is used to absorb voltage spikes and energy at MOSFET turn-off instant, then the MOSFET is protected from avalanche breakdown, but the cost increases, occupied area increases, and the failure rate increases at high temperatures
Solution Approach 1:
The patent implements a closed-loop negative feedback control system where the voltage across the MOSFET is continuously monitored during turn-off. When the voltage exceeds a preset threshold, the feedback signal activates the discharge circuit to release energy from the discharge capacitor, thereby clamping the voltage spike and protecting the MOSFET. This feedback mechanism replaces the passive TVS diode approach with an active controlled system that achieves better protection reliability while reducing component count and occupied area.
2Object-affected harmful factors
If a clamp TVS diode is used to absorb turn-off energy, then voltage spikes are suppressed, but 4 to 5 TVSs are needed which increases cost and requires sufficient heat dissipation copper foils
Solution Approach 1:
The patent employs a discharge capacitor that is charged during MOSFET turn-on and automatically discharged when voltage spikes occur during turn-off. The system uses its own stored energy to counteract the harmful voltage spikes, eliminating the need for external high-power TVS diodes and their associated heat dissipation structures. The discharge capacitor serves dual purposes: energy storage during normal operation and active clamping during transient events.
3Reliability
If TVS diodes are used for voltage clamping, then MOSFET is protected, but the TVS has high short-circuit failure rate and absorption power is greatly affected by temperature
Solution Approach 1:
The patent replaces the passive semiconductor-based TVS diode mechanism with an active electronic control system using operational amplifiers, transistors, and a discharge capacitor. This substitution eliminates the temperature-dependent absorption characteristics of TVS diodes, as the active circuit maintains stable clamping voltage through feedback control regardless of temperature variations. The system achieves temperature-insensitive protection by using electronic control rather than relying on the temperature-sensitive breakdown characteristics of semiconductor junctions.
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 solution effectively limits the drain-source voltage of the MOSFET, reduces the risk of high-temperature failures, and eliminates the need for heat-dissipating structures, thereby addressing the high failure rate and large occupied area issues associated with traditional TVS diode solutions.
Implementation Method 1
a discharge capacitor, connected between a gate connection terminal and a source connection terminal
Implementation Method 2
an overvoltage signal acquisition module, connected between a source connection terminal and a drain connection terminal; the overvoltage signal acquisition module is configured for being turned on when an overvoltage signal is acquired
Implementation Method 3
the negative feedback module gives negative feedback to the discharge current control module when the overvoltage signal acquisition module is turned on, and the discharge current control module controls a discharge current of the discharge capacitor according to the negative feedback
Data Source
AI summary
A soft turn-off active clamp protection circuit and a power system are disclosed. The circuit includes a gate connection terminal, a drain connection terminal, a source connection terminal, a discharge capacitor, an overvoltage signal acquisition module, a negative feedback module, a discharge current control module and a turn-off control module.