Protection Transistor Circuit for High-Voltage Current Measurement
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Solution Overview
Problem
Existing current measurement systems in electrical circuits, particularly those using MOS transistors, face challenges in protecting operational amplifiers when the power transistor is open, especially at high voltages, requiring complex sequencing and being unsuitable for high voltage networks due to limitations in bandwidth and leakage current management.
Innovation Solution
A current measuring device with a protection transistor that remains open until the voltage across the power transistor is safe, using a direct voltage source connected to the gate of the protection transistor and a resistor to limit voltage, allowing automatic control during transient phases and reducing leakage current through a filter and current source, enabling measurement across high voltage networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a series resistor is added upstream of the operational amplifier input to limit leakage current, then the operational amplifier is protected from damage, but the bandwidth of the operational amplifier is limited and the device cannot be used for high voltage networks
Solution Approach 1:
A protection transistor is introduced as an intermediary component between the power transistor and the operational amplifier. This transistor acts as a mediator that blocks high voltage from reaching the operational amplifier while allowing accurate current measurement through its controlled conduction, thereby protecting the amplifier without limiting bandwidth
Solution Approach 2:
The invention changes the electrical parameters (voltage blocking capability, conduction state) of the protection transistor dynamically based on the operating conditions. By controlling the gate voltage of the protection transistor, the system adapts to different voltage levels and current conditions, enabling both protection and high-bandwidth operation
2Reliability
If a contactor is added to limit leakage current during the opening phase of the power transistor, then the operational amplifier is protected, but a complex sequencing is required and synchronization is needed for high voltage
Solution Approach 1:
The protection function is merged with the existing power transistor control circuitry. The protection transistor shares the same control mechanism and timing as the power transistor, eliminating the need for separate contactor control sequences and synchronization logic. This integration simplifies the overall control system while maintaining protection functionality
Solution Approach 2:
The protection transistor automatically responds to the operating state of the power transistor through shared control signals. When the power transistor switches states, the protection transistor self-adjusts its conduction state accordingly, eliminating the need for complex external sequencing and synchronization control
3Measurement precision
If the power transistor is used to measure current through its on-state resistance, then current measurement is achieved, but the measurement circuit must withstand high voltage when the transistor is open
Solution Approach 1:
The measurement system is segmented into two functional parts: the power transistor handles high voltage switching and current conduction, while the protection transistor isolates the measurement circuit from high voltage exposure. This segmentation allows the measurement circuit to operate at safe voltage levels while still measuring the current through the power transistor's on-state resistance accurately
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 allows for safe and accurate current measurement across power transistors in high voltage networks by automatically controlling the protection transistor, reducing leakage current, and enabling detection of overcurrents, thus protecting the utility circuit and ensuring reliable operation.
Implementation Method 1
a first resistor (R1) one of whose terminals is connected to the source of the protection transistor (M2) and the other of whose terminals is connected to ground M
Implementation Method 2
reducing leakage current through a filter and current source
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a protection device (P) for a service circuit (Z) connected to a power electrical circuit comprising a power transistor (M1) incorporated in series in the power electrical circuit and to one terminal of which the service circuit (Z) is connected, characterized in that said protection device (P) further comprises a protection transistor (M2) whose drain is connected to the drain of the power transistor (M1) and whose source is connected to the service circuit (Z), a first DC voltage source (V1) being permanently connected to the gate of the protection transistor (M2), and a first resistor (R1) one of whose terminals is connected to the source of the protection transistor (M2) and the other of whose terminals is connected to ground (M).