Series MOSFET Gate Control via Voltage Clipping
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Solution Overview
Problem
Existing control devices in switching power supply systems, which use multiple MOSFET transistors in series, face challenges in maintaining effective control of the second transistor across varying DC bus voltages without increasing capacitor capacitance, leading to high losses and high costs.
Innovation Solution
A control device with two transistors in series, where the gate of the second transistor is connected to a voltage source and a voltage clipping/switching device, such as a zener diode, ensures sufficient voltage for proper operation of the second transistor, eliminating the need for increased capacitor capacitance and optimizing transistor control across varying voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a single MOSFET transistor with breakdown voltage of 1200V-1700V is used, then the device can switch high voltage, but the transistor operates at technological limits with high cost and high Joule losses
Solution Approach 1:
The patent divides a single high-voltage switching task into two separate MOSFET transistors connected in series. Each transistor handles a portion of the total voltage (e.g., 600V-900V each for a 1200V-1700V system), operating within their optimal breakdown voltage ranges. This segmentation allows each device to work efficiently without exceeding technological limits, reducing individual and total Joule losses while maintaining the required voltage handling capability.
2Loss of energy
If two MOSFET transistors are associated in series with lower breakdown voltages, then optimal MOSFET technology use is achieved, but the control of the second transistor becomes dependent on capacitor characteristics and voltage levels
Solution Approach 1:
The patent introduces a capacitor connected between the gate of the second transistor and the first input terminal as an intermediary element. This capacitor serves dual functions: it provides the necessary load to control the second transistor and limits the voltage across the first transistor to an optimal value. By using this intermediary capacitor, the control of the second transistor is decoupled from direct dependence on DC bus voltage levels, enabling reliable operation across varying voltage conditions.
3Ease of operation
If the capacitance of the capacitor connected to the gate of the second transistor is increased to ensure suitable control, then the second transistor can be controlled at low capacitor terminal voltages, but the capacitance cannot be increased indefinitely
Solution Approach 1:
The patent optimizes the capacitance value of the control capacitor to achieve the minimum necessary capacitance for reliable transistor control. By carefully selecting and adjusting the capacitance parameter, the system achieves effective control of the second transistor without requiring excessive capacitance values. This parameter optimization allows the capacitor to function effectively within practical limits, avoiding the need for indefinitely large capacitance while ensuring proper transistor operation across the full range of DC bus voltages.
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
This solution allows for reliable control of the second transistor across a wide range of DC bus voltages, reducing losses and costs by eliminating the need for increased capacitance, thereby enhancing the efficiency and performance of the switching power supply system.
Implementation Method 1
it has in particular been proposed to replace the capacitor with a zener diode Dz1, which then makes it possible to fix the voltage across the terminals of the first transistor T1
Implementation Method 2
the control of the second transistor T2 is then ensured thanks to the charge stored by the intrinsic capacitance (Ci) of the zener diode Dz1
Implementation Method 3
the control device may comprise a single MOSFET type transistor having a breakdown voltage of between 1200 V and 1700 V
Implementation Method 4
it is known to associate two MOSFET transistors in series, having lower breakdown voltages, ranging from 600V to 900V. Each of the two transistors in series thus supports a lower electrical voltage
Data Source
Figure 1A~3
Figure 4A~4E
Figure 5~6
AI summary
The device (1) has an input terminal (A) i.e. MOSFET, and another input terminal (B), and a transistor (T1) that is connected to the latter input terminal. A gate (G) is provided to receive control signal originating from a control unit (U). Another transistor (T2) is connected to the former input terminal in series with the former transistor. A control assembly is connected to a floating control gate of the latter transistor and to the latter input terminal. The control assembly comprises a voltage source (Vdc) and a voltage clamping/routing device connected to the voltage source. Independent claims are also included for the following: (1) a switched electrical power supply system (2) a variable speed transmission.