Series MOSFET Switch Circuit for High Voltage Control
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Solution Overview
Problem
Existing high-voltage switch circuits using MOSFETs face challenges in performing switching beyond their withstand voltage and achieving complete voltage lowering to ground, as they require sufficient voltage for ON/OFF control and are prone to transistor elements turning off due to gate-to-source voltage drops.
Innovation Solution
A switch circuit design with multiple transistor elements connected in series, where the source of one element is connected to the drain of another between high voltage and system ground, allowing for ON/OFF control and complete voltage lowering by using a resistor in parallel between the gate and source of specific transistor elements, enabling reliable high-voltage switching without exceeding the MOSFETs' withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple transistor elements are connected in series to handle high voltage, then the voltage applied to each transistor element is reduced to one n-th, but ON/OFF control cannot be performed unless sufficient voltage is kept to be applied to the high voltage side
Solution Approach 1:
The high voltage switch is segmented into multiple transistor elements connected in series, with each element handling a portion of the total voltage. The control circuit is also segmented to independently control each transistor element's gate, allowing precise voltage distribution and control even when high voltage is not applied to the entire circuit.
Solution Approach 2:
A control circuit acts as an intermediary between the control signal and the transistor elements. It generates appropriate gate voltages for each transistor element based on the desired switch state, enabling reliable ON/OFF control without requiring sufficient voltage to be maintained on the high voltage side throughout the entire circuit.
2Ease of operation
If all transistor elements are turned on and grounded to lower the high voltage side to ground potential, then the voltage on the high potential side should be lowered to ground, but the transistor element on the highest potential side turns off due to gate-to-source voltage drop, releasing the grounded state
Solution Approach 1:
The control circuit monitors the state of each transistor element and adjusts the gate voltages accordingly. When lowering voltage to ground, the control circuit ensures that gate-to-source voltages remain sufficient to maintain the ON state of all transistor elements, preventing premature turn-off and ensuring stable grounded state.
Solution Approach 2:
Before attempting to ground the high voltage side, the control circuit preliminarily adjusts the gate voltages of all transistor elements to ensure they remain in the ON state throughout the voltage lowering process. This preliminary adjustment prevents the gate-to-source voltage drop from causing unintended turn-off of the transistor element on the highest potential side.
Data Source
AI summary
To provide a switch circuit in which ON/OFF control can be realized even in a state where high voltage is not applied, and high voltage can be completely lowered to the ground.Provided is a switch circuit that includes plural MOS switches connected in series in such a manner that the source of one element is connected to the drain of another between high voltage and a system ground and that switches a connection state between the high voltage and the system ground, the switch circuit including: a MOS switch 101 the source of which is connected to the system ground among the plural MOS switches; a MOS switch 102 the source of which is connected to the drain of the MOS switch 101 in a shared manner and the drain of which is connected to the high voltage side among the plural MOS switches; a MOS switch 103 the drain of which is connected to the gate of the MOS switch 102 in a shared manner; and a resistor 104 that is connected in parallel between the gate and the source of the MOS switch 102.