Power Semiconductor Device Surge Protection Circuit
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Solution Overview
Problem
The existing power semiconductor devices are prone to heat destruction due to surge voltages when a steep increase in power supply voltage occurs during the turn-off condition, leading to potential damage of the output transistor.
Innovation Solution
A power semiconductor device configuration that includes an output transistor, a control circuit, a low-speed discharge route, and a high-speed discharge route, with a countercurrent prevention device, allowing for controlled discharging and preventing the output transistor from turning on during steep power supply voltage increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the output transistor is turned off rapidly by activating the discharge transistor, then the turn-off speed is improved, but the device becomes vulnerable to heat destruction during steep power supply voltage increases
Solution Approach 1:
The countercurrent prevention device applies preliminary anti-action by blocking the harmful current flow path before the current can cause damage. When the power supply voltage increases steeply during turn-off, the device prevents the current from flowing through the discharge transistor's source to the gate, thereby preventing the output transistor from turning on and avoiding heat destruction.
Solution Approach 2:
The countercurrent prevention device acts as an intermediary element between the discharge transistor's source and gate. It selectively controls current flow by blocking the harmful reverse current while allowing normal discharge operation, thus mediating between the need for rapid turn-off and protection against voltage surges.
2Speed
If the discharge transistor is used for rapid discharge, then the turn-off speed is improved, but the circuit complexity increases due to additional components
Solution Approach 1:
The countercurrent prevention device serves multiple functions: it enables rapid discharge during normal operation, prevents heat destruction during voltage surges, and maintains the output transistor's off state during abnormal conditions. By integrating these functions into a single device, the overall circuit complexity is minimized while achieving multiple protective and operational goals.
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
Prevents heat destruction of the output transistor by ensuring it remains off even during steep increases in power supply voltage, thereby enhancing the device's reliability and longevity.
Implementation Method 1
an anode and cathode of the zener diode 250 are connected with the node N2 and the ground terminal TG, respectively... a current flows from the node N1 to the ground terminal TG through the discharge transistor 240 and the zener diode 250
Implementation Method 2
The discharge transistor 240 has a parasitic bipolar transistor of a vertical type... a parasitic capacitance (capacitance between the collector and the base) C1 is generated between the power supply terminal TV and the node NC
Data Source
AI summary
A power semiconductor device includes an output transistor, a control circuit connected with a gate of the output transistor, a first discharge route from a first node to a ground terminal, and a second discharge route from the first node to the ground terminal. In a usual turn-off, only the first discharge route is used. When a load abnormality occurs, both of the first and second discharge routes are used. The second discharge route contains a discharge transistor and a countercurrent prevention device. The discharge transistor is connected between the first node and the second node. The countercurrent prevention device prevents a flow of current from the third node to the second node. At least, in an OFF period, the control circuit sets the gate voltage of the discharge transistor to a high level.