Series MOSFET Gate Control via Zener Diode Voltage Regulation
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Solution Overview
Problem
Existing control devices in switching power supply systems, which use two MOSFET transistors in series, face challenges in maintaining effective control of the second transistor across varying main DC voltages without increasing capacitor capacitance, leading to high losses and costs due to the reliance on capacitance and voltage levels.
Innovation Solution
A control device with two transistors in series, where each transistor has a gate-connected capacitor and zener diodes to self-power the gate of the second transistor, allowing for adaptive voltage control without increasing capacitance, using a cascaded pattern of capacitors and zener diodes to maintain optimal voltage across each transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two MOSFET transistors are associated in series with lower breakdown voltages, then the compatibility with optimal MOSFET technology is improved, but the control of the second transistor becomes dependent on capacitance and voltage level
Solution Approach 1:
A zener diode is introduced as an intermediary component between the capacitor and the gate of the second transistor. The zener diode regulates the voltage across the capacitor, ensuring that the gate of the second transistor receives a controlled voltage level independent of the DC bus voltage variations. This mediator component decouples the control dependency on capacitance and voltage level.
Solution Approach 2:
The invention changes the voltage parameter across the capacitor by introducing a zener diode that maintains a fixed voltage across the capacitor regardless of the DC bus voltage. This parameter change ensures that the gate of the second transistor is controlled by a stable voltage level, making the control independent of capacitance value and DC bus voltage variations.
2Ease of operation
If the capacitance of the capacitor is increased to control the second transistor at low voltage, then the control effectiveness is improved, but the capacitance cannot be increased indefinitely
Solution Approach 1:
Instead of increasing capacitance to improve control effectiveness, the invention changes the voltage parameter by introducing a zener diode. The zener diode ensures that the voltage across the capacitor remains fixed at the zener voltage level, providing effective gate control without requiring large capacitance values. This parameter change resolves the contradiction between control effectiveness and capacitance limitations.
Solution Approach 2:
The zener diode acts as a voltage regulation element that replaces the need for large capacitance values. By using a simple zener diode component, the invention achieves effective transistor control without the complexity and size associated with large capacitors, effectively using a simpler component to replace a more complex solution.
3Ease of operation
If a zener diode is used to fix the voltage across the first transistor, then the voltage control is improved, but the control of the second transistor still depends on parasitic capacitance
Solution Approach 1:
An additional zener diode is introduced as an intermediary component specifically for controlling the gate of the second transistor. This second zener diode acts as a voltage regulator that ensures the gate of the second transistor receives a stable voltage level, making the control independent of the parasitic capacitance of the first zener diode. The mediator component decouples the control dependency on parasitic capacitance.
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 enables effective control of the second transistor across a wide range of DC voltages, reducing losses and costs by utilizing self-powered capacitors and zener diodes to maintain optimal voltage, thus improving efficiency and reducing the need for increased capacitance.
Implementation Method 1
A capacitor C1 is connected between the gate of the second transistor T2 and the first input terminal A. The role of the capacitor C1 is twofold: provide enough load to control the second transistor
Implementation Method 2
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
Data Source
Figure 1A~3
Figure 4~5A
Figure 5B~5C
AI summary
The device (1) has a first transistor (T1) connected to a first input terminal (B) and provided with a gate (G) to receive control signals from a control unit (U). A second transistor (T2) is connected to a second input terminal (A) by its drain (D) and to the first transistor through its source (S). A control assembly is connected to a gate of the second transistor and to the first input terminal and includes a voltage clipping/routing device connected in series to a capacitor (Ca). A Zener diode (Dz2) is connected between the gate and the source of the second transistor. The transistor is a MOSFET or Insulated gate bipolar transistor (IGBT). An independent claim is also included for a variable speed drive to control an electrical load.