MOSFET Rectifier Gate Voltage Boost for Load Dump
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Solution Overview
Problem
Autonomous type synchronous rectification MOSFETs with a pair of external terminals face challenges in on/off control and energy consumption during a load dump, making it difficult to prevent current flow and maintain voltage levels, leading to insufficient gate driving due to capacitor charge deficiency.
Innovation Solution
A rectifier circuit with a MOSFET, control circuit, power source, and hold circuit that boosts the gate voltage of the MOSFET when an internal trigger voltage is met, allowing the MOSFET to maintain an ON state and manage energy consumption during a load dump by circulating current in a bridge circuit and generator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an autonomous type synchronous rectification MOSFET with a pair of external terminals is used, then the number of external terminals is reduced and cost is lowered, but it becomes difficult to perform on/off control and detect abnormal voltage during load dump
Solution Approach 1:
The MOSFET performs autonomous synchronous rectification by using its own source-drain voltage to control its on/off state. The control circuit detects the voltage between source and drain terminals and automatically adjusts the gate voltage accordingly, eliminating the need for external sensors or controllers. This self-service mechanism resolves the contradiction by maintaining full control capability while reducing external terminal requirements.
2Device complexity
If the MOSFET is controlled by detecting source-drain voltage internally, then sensor and control circuit complexity is reduced, but it becomes difficult to detect abnormal voltage during load dump
Solution Approach 1:
The control circuit is designed to perform multiple functions: normal rectification control by detecting source-drain voltage, and abnormal voltage detection during load dump conditions. By making the control circuit universal and multi-functional, the patent resolves the contradiction between simplicity and reliability, as the same simplified circuit handles both standard operation and fault detection without requiring additional sensors.
3Reliability
If energy during load dump is consumed by circulating current in bridge circuit and generator, then high voltage output is prevented, but capacitor charge is depleted and MOSFET gate driving becomes insufficient
Solution Approach 1:
The patent implements periodic switching of the MOSFET during load dump conditions to manage energy consumption. By periodically turning the MOSFET on and off, the system dissipates energy through controlled current circulation while allowing the capacitor to recharge during off periods. This periodic action resolves the contradiction by balancing energy dissipation with charge replenishment, maintaining both overvoltage protection and sufficient gate driving capability.
4Reliability
If the MOSFET is turned on during load dump to consume energy, then through current is prevented, but gate voltage becomes insufficient due to capacitor charge deficiency
Solution Approach 1:
The control circuit monitors capacitor charge levels and predicts when charge deficiency will occur before it actually happens. When approaching the charge depletion threshold, the circuit preliminarily adjusts the MOSFET switching strategy or gate voltage levels to prevent complete charge exhaustion. This preliminary action ensures that the MOSFET can be turned on when needed for current control while maintaining sufficient gate driving power throughout the operation.
Data Source
AI summary
A rectifier includes a rectification MOSFET that performs rectification, a comparator formed by connecting a drain of the rectification MOSFET to a non-inverting input terminal and a source to an inverting input terminal, and a control circuit that performs an on/off control of the rectification MOSFET using an output of the comparator. The control circuit includes a shut-off MOSFET that disconnects a drain of the rectification MOSFET and a non-inverting input terminal of the comparator from each other, and a shut-off circuit that turns off the shut-off MOSFET to electrically disconnect the drain of the rectification MOSFET and the non-inverting input terminal of the comparator from each other when the drain voltage of the rectification MOSFET is equal to or higher than a predetermined first voltage.