High-Voltage MOSFET Stage Using Inductor-Assisted Self-Drive
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Solution Overview
Problem
Short-channel CMOS devices have low breakdown voltage, making them unsuitable for high voltage power-conversion regulators, and they incur significant power loss due to high gate-charge, which reduces the efficiency of DC-DC converters.
Innovation Solution
The implementation of a buck converter with a stacked MOSFET structure where power MOSFETs are self-driven without driver circuits, and some MOSFETs undergo partial gate charge/discharge through the output inductor to minimize power loss, using a cascode output stage with low side and high side transistors to achieve efficient high voltage conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If short-channel CMOS devices are used in high voltage power-conversion regulators, then device integration is achieved, but breakdown voltage is insufficient and gate-charge power loss increases
Solution Approach 1:
The power converter stage is segmented into multiple stacked power MOSFETs (first through fourth high side power MOSFETs and first through fourth low side power MOSFETs) connected in series between the positive and negative power supplies. This segmentation allows each individual MOSFET to withstand only a fraction of the total voltage, enabling the use of low-voltage short-channel CMOS devices in a high-voltage application while maintaining device integration.
Solution Approach 2:
Bias voltage generators are introduced as intermediary components to provide appropriate gate drive voltages to each stacked MOSFET. The high side bias voltage generator generates a high side bias voltage, and the low side bias voltage generator generates a low side bias voltage, enabling independent control of each MOSFET's gate terminal. This intermediary control mechanism resolves the voltage mismatch between low-voltage CMOS devices and high-voltage power conversion requirements.
2Device complexity
If short-channel CMOS devices are used in DC-DC converters, then integration is improved, but gate-charge causes significant power loss reducing efficiency
Solution Approach 1:
The gate charges and discharges of the stacked power MOSFETs are performed periodically through the output inductor during switching transitions. Instead of continuous charging from dedicated driver circuits, the gate capacitances are charged and discharged periodically through the inductor, converting what would be continuous power loss into periodic energy transfer that contributes to the power conversion function.
Solution Approach 2:
The output inductor serves a dual function: it performs its primary power transfer function while simultaneously providing gate charge/discharge paths for the stacked MOSFETs. This self-service approach eliminates the need for separate driver circuits, reducing overall system power loss while maintaining device integration.
3Reliability
If stacked MOSFET structure is implemented, then high voltage conversion is achieved, but driver circuit complexity increases
Solution Approach 1:
The driver circuit functions are merged with the power stage components. The output inductor is combined with the gate drive function, and the bias voltage generators are integrated into the power stage. This merging eliminates separate driver circuits while maintaining the ability to drive stacked MOSFETs at high voltages, thereby reducing overall driver circuit complexity.
Solution Approach 2:
The output inductor performs multiple functions: it serves as the power transfer element in the power conversion circuit and simultaneously acts as the gate charge/discharge path for the stacked MOSFETs. The bias voltage generators also serve dual purposes by providing both voltage level shifting and gate drive control. This multi-functionality reduces the need for separate dedicated driver circuits.
Data Source
AI summary
A power converter is disclosed. The power converter includes a positive power supply, an output node, first, second, and third high side transistors serially connected between the positive power supply and the output node, and a high side bias voltage generator configured to generate a high side bias voltage. A gate of the second high side transistor is connected to the high side bias voltage generator. The power converter also includes a signal driver configured to selectively connect a gate of the first transistor to either the positive power supply or the high side bias voltage generator, a switch configured to selectively connect a gate of the third transistor to the high side bias voltage generator, and a capacitor connected to the gate of the third transistor and to a source of the second high side transistor.