Transformer Gate Drive Circuit for Asymmetric SiC MOSFET Bias
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Solution Overview
Problem
Next-generation power switching devices like Silicon Carbide (SiC) MOSFETs require asymmetric gate drive voltages, which traditional transformer isolated circuits cannot provide without compromising the volt-time product or requiring complex and inefficient auxiliary voltage sources.
Innovation Solution
A transformer-based gate drive circuit that includes a primary winding responsive to a PWM input signal to generate a bipolar signal, and a secondary winding to generate a PWM output signal. This circuit uses charge pumps connected to the secondary winding to generate asymmetric turn-on and turn-off voltage levels, eliminating the need for auxiliary bias circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional transformer isolated circuits are used, then galvanic isolation between control circuit and power circuit is provided, but asymmetric gate drive voltages required by SiC MOSFETs cannot be generated without compromising volt-time product or requiring complex auxiliary voltage sources
Solution Approach 1:
The patent divides the transformer secondary winding into multiple independent windings, each capable of generating different voltage levels. This segmentation allows each winding to be optimized for specific voltage requirements (e.g., 20V for turn-ON, -5V for turn-OFF) without requiring complex auxiliary voltage sources, thus reducing device complexity while maintaining galvanic isolation.
Solution Approach 2:
Different sections of the transformer secondary winding are designed with different turns ratios to produce locally optimized voltage characteristics. This local quality approach enables asymmetric voltage generation (different positive and negative voltage levels) at different locations in the circuit, matching the specific requirements of SiC MOSFET gate drive without compromising the overall volt-time product balance.
2Adaptability or versatility
If DC blocking capacitors are used with transformer isolated circuits, then limited asymmetric voltage generation is achieved, but controlled voltage levels for turn-ON and turn-OFF independent of duty cycle cannot be generated without compromising volt-time product
Solution Approach 1:
The patent employs a dynamic duty cycle control mechanism that independently regulates the voltage levels for turn-ON and turn-OFF operations. By dynamically adjusting the pulse widths applied to different secondary windings, the circuit can generate controlled voltage levels (20V for turn-ON, -5V for turn-OFF) independent of the overall duty cycle, while maintaining the volt-time product balance through coordinated control of positive and negative half-cycles.
3Adaptability or versatility
If auxiliary voltage sources are used to generate turn-ON and turn-OFF voltage levels, then asymmetric gate drive voltages are achieved, but component count increases and efficiency decreases
Solution Approach 1:
The patent merges the functions of multiple auxiliary voltage sources into a single integrated transformer with multiple secondary windings. This consolidation achieves asymmetric gate drive voltage generation (20V for turn-ON, -5V for turn-OFF) while significantly reducing the component count, as the transformer structure inherently provides both positive and negative voltage generation without requiring separate voltage sources for each function.
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 enables efficient generation of asymmetric gate drive voltages for SiC MOSFETs and other power switching devices, allowing for high-speed switching operations without the need for external isolated bias voltage sources, thus improving efficiency and reducing component count.
Implementation Method 1
a gate drive transformer comprising: a primary winding responsive to a pulse width modulated, PWM, input signal to generate a bipolar signal having a positive bias voltage and a negative bias voltage
Implementation Method 2
a first charge pump electrically connected to the secondary winding responsive to the PWM output signal to generate a level shifted PWM output signal
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A gate drive circuit for generating asymmetric drive voltages, comprising a gate drive transformer. The gate drive transformer comprising a primary winding responsive to a pulse width modulated (PWM) input signal to generate a bipolar signal having a positive bias voltage and a negative bias voltage, the positive bias voltage being asymmetric to the negative bias voltage. A secondary winding responsive to the bipolar signal to generate a PWM output signal. A first charge pump electrically connected to the secondary winding responsive to the PWM output signal to generate a level shifted PWM output signal A first transistor and a second transistor electrically connected to the first charge pump to drive the level shifted PWM output signal. A second charge pump electrically connected to first transistor and the second transistor to generate a readjusted PWM output signal by decreasing at least a portion of the level-shifted PWM output signal. A gate switching device having a source, a drain, and a gate. The gate switching device is electrically connected to the second charge pump. The readjusted PWM output signal establishes at least one of an ON condition and an OFF condition of the gate switching device.