MOSFET Rectifier Switching Control via Parasitic Diode Timing
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Solution Overview
Problem
MOSFETs in motor vehicle rectifiers experience undesirable power loss and overheating due to uncontrolled switching off caused by small voltage drops during conductive phases, leading to inefficient energy conversion.
Innovation Solution
Implementing a timing-controlled actuation method for MOSFETs in rectifiers, where the switch-off signal is provided after a prescribed period determined by the voltage drop across the parasitic diode, ensuring a sufficient voltage is maintained above 400 mV, and adjusting the alterable time interval based on rotation speed fluctuations using a regulatory algorithm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the MOSFET switching is controlled by measuring voltage drop during conductive phase, then the MOSFET can be actuated before parasitic diode becomes conductive, but small voltage drops (few mV) cause disturbances leading to uncontrolled switch-off and high power loss
Solution Approach 1:
The patent applies preliminary action by determining the switch-off time in advance based on the measured period time from voltage zero-crossing to parasitic diode conduction. This pre-calculated time interval is stored and used to generate the switch-off signal, avoiding the need to measure small voltage drops during the conductive phase when the MOSFET is already on. The switch-off timing is decided before the conductive phase begins, preventing disturbances from causing uncontrolled switch-off.
Solution Approach 2:
The patent uses the parasitic diode's forward voltage as an intermediary indicator to determine switching timing. Instead of directly measuring the small voltage drop across the conducting MOSFET (which is unreliable), the system measures the voltage when the parasitic diode becomes conductive - a much larger, easily detectable voltage signal. This intermediary measurement provides a reliable reference point for calculating the optimal switch-off time.
2Device complexity
If a fixed time interval is used for MOSFET switching, then the control is simple, but it cannot react quickly to rotation speed fluctuations causing excessive current flow
Solution Approach 1:
The patent applies dynamics by making the switching time interval variable rather than fixed. The control system continuously measures the period time between voltage zero-crossing and parasitic diode conduction, which varies with rotation speed. This measured period time dynamically adjusts the switch-off timing, allowing the system to react quickly to rotation speed fluctuations. When rotation speed changes, the period time changes, and the switch-off time is automatically adjusted accordingly, preventing excessive current flow while maintaining relatively simple control logic.
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 reduces power loss, allows quick reaction to rotation speed changes, minimizes MOSFET size requirements, and prevents reverse currents, thereby enhancing the efficiency and reliability of the rectifier.
Implementation Method 1
the voltage drop across the parasitic diode of the respective MOSFET. This MOSFET is switched off after a prescribed time
Data Source
AI summary
The invention relates to a method for actuating the switching transistors of a rectifier which is provided for converting the phase voltages that are provided by a vehicle generator into a direct current voltage. Each switching transistor comprises a parasitic diode. An activation signal for initiating the conducting phase and a de-activation signal for ending the conducting phase are supplied to each control terminal of the switching transistors. A timer is started simultaneously with the provision of an activation signal and the de-activation signal is provided once a predetermined time period has passed.