Half-Bridge Circuit Using Bidirectional Transistor Diode Function
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Solution Overview
Problem
Traditional bridge circuits require separate anti-parallel diodes for proper operation, which lead to increased complexity and power dissipation due to the inherent poor switching characteristics of parasitic diodes, and are prone to shoot-through currents from high-voltage supplies.
Innovation Solution
A half bridge circuit design utilizing a single transistor that can operate in multiple modes to block voltage, conduct current in both directions, and function as both a switching transistor and a diode, eliminating the need for separate anti-parallel diodes and minimizing power dissipation by controlling gate voltages to prevent shoot-through currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate anti-parallel diodes are added to each transistor switch, then proper operation of the bridge circuit is achieved, but device complexity increases
Solution Approach 1:
The patent merges the function of the transistor switch and the anti-parallel diode into a single integrated device. The integrated switch contains both the N-channel MOSFET and the anti-parallel diode as separate but combined components, eliminating the need for external diodes and reducing overall circuit complexity while maintaining proper bridge circuit operation.
Solution Approach 2:
The integrated switch performs multiple functions simultaneously: it acts as both a voltage switching element and a freewheeling diode. This multi-functional device replaces what traditionally required two separate components (transistor + diode), thereby reducing device complexity while ensuring reliable bridge circuit operation.
2Reliability
If parasitic diodes are used in MOS transistors, then the circuit operates, but power dissipation increases due to poor switching characteristics
Solution Approach 1:
The patent extracts the diode function from the parasitic diode inherent in the MOSFET and implements it as a dedicated, optimally designed anti-parallel diode within the integrated switch. This allows the diode to be specifically designed for low-loss operation rather than being a byproduct of the transistor structure, thereby reducing power dissipation while maintaining circuit operation.
Solution Approach 2:
The patent changes the parameters of the diode by using a Schottky diode with optimized characteristics (lower forward voltage drop, faster switching) compared to the parasitic diode. This parameter optimization reduces power dissipation during freewheeling operation while ensuring reliable circuit operation.
3Productivity
If transistors are switched on and off rapidly, then motor control precision is improved, but shoot-through currents occur from high-voltage supplies
Solution Approach 1:
The patent implements preliminary action by providing controlled turn-on and turn-off sequences for the transistors. The gate drive circuitry ensures that one transistor is fully off before the other is turned on, and that body diodes are properly reverse-biased before voltage transitions. This preliminary control prevents shoot-through currents while maintaining rapid switching for precise motor control.
Solution Approach 2:
The patent uses feedback mechanisms in the gate drive circuitry to monitor transistor states and control switching timing. This feedback ensures that switching transitions are coordinated to prevent both transistors from being on simultaneously, eliminating shoot-through currents while enabling high-precision motor control through optimized PWM switching.
Data Source
AI summary
A half bridge is described with at least one transistor having a channel that is capable in a first mode of operation of blocking a substantial voltage in at least one direction, in a second mode of operation of conducting substantial current in one direction through the channel and in a third mode of operation of conducting substantial current in an opposite direction through the channel. The half bridge can have two circuits with such a transistor.