Cascode Circuit With Mediated Gate Control for Switching Speed
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Solution Overview
Problem
Conventional cascode circuits with normally-on and normally-off transistor devices face challenges in controlling switching speed and complexity, particularly in controlling the normally-on transistor device, which can lead to uncontrolled current flow and increased manufacturing costs due to the need for independent drive signals and complex drive circuits.
Innovation Solution
A cascode circuit design where a normally-on transistor device and a normally-off transistor device are connected in series, with a third transistor device and a voltage source in parallel, allowing for independent control of the normally-off transistor device to govern the switching state of the normally-on device, reducing complexity and manufacturing costs while maintaining control over switching speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a normally-on transistor device is used in a cascode circuit, then manufacturing cost is reduced and manufacturing simplicity is improved, but control over the normally-on transistor device becomes difficult and switching speed control is compromised
Solution Approach 1:
A third transistor device is introduced as an intermediary element connected in series with the normally-on transistor device. This third transistor acts as a mediator that controls the drive voltage applied to the normally-on transistor, enabling indirect control of its switching state. The intermediary transistor receives control signals and regulates the voltage applied to the normally-on transistor's gate, thus solving the control difficulty while maintaining the manufacturing advantages of normally-on devices.
2Speed
If independent drive signals are used for normally-on and normally-off transistor devices, then switching speed control is improved, but drive circuit complexity increases
Solution Approach 1:
The drive circuits for the normally-on and normally-off transistor devices are merged into a unified control structure. The third transistor device serves as a common control element that simultaneously manages the drive signals for both transistor types. By combining the control functions into a single integrated drive circuit rather than using separate independent drive circuits, the complexity is reduced while maintaining the ability to control switching speeds of both devices.
3Ease of manufacture
If a normally-on transistor device is connected in series with a load during start-up, then uncontrolled current flow occurs, but using a normally-off transistor device increases manufacturing cost
Solution Approach 1:
The third transistor device is activated in advance during the start-up sequence to establish controlled current flow before the normally-on transistor device is fully engaged. This preliminary action ensures that the circuit is properly initialized with controlled current, preventing uncontrolled current flow scenarios. The third transistor acts as a protective element that is activated first to set up safe operating conditions.
Solution Approach 2:
The third transistor device serves as an intermediary protective element between the power source and the normally-on transistor device during start-up. It mediates the current flow by being activated first to establish controlled pathways, preventing direct uncontrolled current flow through the load. This intermediary approach maintains reliability while allowing the use of cost-effective normally-on transistor devices.
Data Source
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AI summary
An electronic circuit, a half-bridge circuit, a power converter, and a method are disclosed. The electronic circuit includes a switching circuit (10). The switching circuit (10) includes a first transistor device (1) with a control node (11) and a load path between a first load path node (12) and a second load path node (13), a second transistor device (2) with a control node (21) and a load path between a first load path node (22) and a second load path node (23), and a series circuit with a third transistor device (3) and a voltage source (4) connected in series with a load path of the third transistor device (3). The first transistor device (1) is a normally-on device, the second transistor device (2) is a normally-off device, and the load paths of the first and second transistor devices (1, 2) are connected in series. The load path of the second transistor device (2) is connected between the control node (11) and the first load path node (12) of the first transistor device (1), and the series circuit is connected in parallel with the load path of the second transistor device (2).