Driver Circuit Arm Short Prevention Using Normally-Off Switch
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Solution Overview
Problem
Inverter circuits using normally-on devices are prone to arm short conditions during startup or power shutdown, leading to potential short-circuit currents, and existing solutions fail to maintain the off-state when the second power source is broken or malfunctions.
Innovation Solution
A driver circuit design incorporating a normally-off third switching element between the second switching element and the power supply, along with control circuits that manage operating voltages and resistors to ensure the third switching element turns off when necessary, preventing arm short by maintaining the off-state during startup or power shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If normally-on switching elements are used in the driver circuit, then high-speed switching and low on-resistance characteristics are achieved, but arm short occurs during startup or power shutdown when control power is not supplied
Solution Approach 1:
A second switching element with normally-off characteristic is introduced as an intermediary between the power supply and the normally-on switching elements. This intermediary element ensures that the normally-on switching elements remain in off-state when control power is not supplied, preventing arm short while allowing them to operate at full speed when enabled.
Solution Approach 2:
The control circuits are designed to supply control signals to the second switching elements in advance before startup or during power shutdown conditions. This preliminary action ensures the switching elements are in the desired off-state before the normally-on elements become active, preventing arm short conditions.
2Reliability
If a second power source is added to maintain off-state during power shutdown, then arm short is prevented, but device complexity increases
Solution Approach 1:
The second switching elements serve multiple functions: they act as protection switches during startup and shutdown, and as normal switching elements during operation. This multi-functionality reduces the need for separate protection circuits, thereby limiting the increase in device complexity.
Solution Approach 2:
The protection function and switching function are merged into a single second switching element. By combining these functions, the circuit avoids the need for separate protection components, reducing overall complexity while maintaining reliability.
3Power
If normally-on devices are used, then excellent characteristics such as high-speed switching and low on-resistance are achieved, but the devices remain in on-state when control signal is not inputted, causing potential short-circuit current
Solution Approach 1:
The second switching element with normally-off characteristic serves as a mediator that controls the power supply to the normally-on switching elements. When control signal is not inputted, this intermediary ensures the normally-on elements are disconnected from power, effectively controlling the off-state while preserving the low on-resistance characteristic when active.
Solution Approach 2:
The control circuits provide control signals to the second switching elements in advance to ensure they are in the off-state before the normally-on elements become active. This preliminary action establishes proper operating conditions, making the system easier to control despite the normally-on characteristic of the main switching elements.
Data Source
AI summary
The present invention provides a safe circuit that can prevent an arm short, when a half-bridge circuit is configured by using a normally-on switching element, and the half-bridge circuit is used as a driver circuit or an inverter circuit. In a driver circuit configured by a half-bridge circuit in which one of input and output terminals of a first switching element 14 is connected to a first power-supply voltage V1 on a high-voltage side, and the first switching element 14 and a second switching element 15 are connected in series, a normally-off third switching element 16 is inserted between the second switching element 15 and a second power-supply voltage V2 on a low voltage side. The third switching element 16 is turned off, when an operating voltage VH or VL supplied from control-circuit power supplies 13a and 13b is insufficient for the operation of a control circuit 11.