Series Transistor Switching Circuit for Reducing Turn-Off Transient Current
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Solution Overview
Problem
Switching circuits with high-withstand-voltage normally-on transistors and low-withstand-voltage normally-off transistors connected in series experience significant transient current and switching losses during turn-off, leading to increased noise and potential transistor breakage.
Innovation Solution
A switching circuit design that includes a high-withstand-voltage normally-on transistor and a low-withstand-voltage normally-off transistor connected in series, with additional diodes and a driving circuit that controls the transistors to manage inductance and voltage thresholds, reducing transient current by routing current through paths with lower inductance and forward voltage, and using internal diodes and protection diodes to prevent excessive voltage application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a high-withstand-voltage normally-on transistor and a low-withstand-voltage normally-off transistor are connected in series, then the circuit can handle high voltage, but large transient current flows at turn-off time
Solution Approach 1:
The gate of the first transistor is connected to the third node through a capacitor, which preliminarily charges the gate capacitance. When the second transistor turns off and the third node voltage rises, the capacitor maintains the gate voltage, ensuring the first transistor turns off promptly and preventing large transient current flow.
Solution Approach 2:
A capacitor is introduced as an intermediary element between the third node and the gate of the first transistor. This capacitor mediates the voltage transfer, ensuring that the gate voltage follows the third node voltage changes, thereby controlling the first transistor's switching timing to reduce transient current.
2Loss of energy
If the first transistor is immediately switched off when the potential of the node rises, then the transient current duration is reduced, but the gate voltage control becomes critical
Solution Approach 1:
The capacitor connected between the third node and the gate of the first transistor provides self-service by automatically charging and discharging according to the voltage changes at the third node. This self-charging mechanism ensures the first transistor turns off at the appropriate time without requiring additional active control circuitry.
3Ease of operation
If diodes are added in reverse parallel to the second transistor, then current path control is improved, but the device complexity increases
Solution Approach 1:
Diodes are added in reverse parallel to the second transistor to utilize the natural diode recovery characteristics. When the second transistor turns off, the diodes provide controlled current paths that prevent voltage spikes and reduce transient current, converting the potential harm of abrupt switching into a beneficial controlled transition.
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 effectively reduces transient current and switching losses during turn-off, preventing transistor breakage and improving the stability and efficiency of the switching circuit, while also reducing high-frequency oscillations and conduction losses.
Implementation Method 1
a capacitor connected between the third node and a gate of the first transistor
Implementation Method 2
a first diode that is provided in reverse parallel to the second transistor on a first path connecting the second and third nodes; a second diode that is provided in reverse parallel to the second transistor on a second path connecting the second and third nodes
Data Source
AI summary
A high-withstand-voltage normally-on transistor and a low-withstand-voltage normally-off transistor are connected in series, and diodes are provided in reverse parallel to the transistor. A gate terminal of the transistor is connected to a source terminal of the transistor, and a gate driving circuit that outputs a control signal to a gate terminal of the transistor is provided. Forward voltage of the diode is made lower than forward voltage of the diode, and an inductance component of a path connecting nodes via the diode is made greater than an inductance component of a path connecting the nodes via the diode. Accordingly, a switching circuit which includes transistors connected in series and in which transient current at a time of turning off is reduced is provided.