Battery Discharge FET Gate Control via Intermediate Voltage Switch
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Solution Overview
Problem
Conventional battery pack configurations face issues with high gate voltage requirements for discharge FETs due to multiple batteries connected in series, leading to limited component selection and extended cutoff times due to increasing drain-source resistance.
Innovation Solution
Incorporating a semiconductor switch controller with a third switch element between the gate of the discharge FET and an intermediate voltage point, allowing for a lower gate withstand voltage FET to be used while ensuring high-speed cutoff by applying a potential from the intermediate voltage via the third switch element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple batteries are connected in series to achieve high voltage output, then the output voltage of the battery pack increases, but the gate withstand voltage requirement for the discharge FET increases
Solution Approach 1:
The gate control voltage is segmented into multiple levels: a first control voltage (e.g., 0V or ground) applied during normal operation, and a second control voltage (e.g., negative voltage) applied during shutdown. This segmentation allows the discharge FET to operate at low gate voltage during normal use while providing sufficient gate control during shutdown, eliminating the need for high gate withstand voltage components.
Solution Approach 2:
The control circuit preliminarily prepares the gate voltage state before shutdown occurs. By detecting the shutdown state in advance and preemptively applying the appropriate gate control voltage, the system ensures that the discharge FET is properly controlled during the transition to shutdown, preventing voltage spikes that would require higher gate withstand voltage ratings.
2Reliability
If the discharge FET is turned off by increasing drain-source resistance, then the discharge path is cut off, but the cutoff time is extended due to voltage division effects
Solution Approach 1:
The control circuit continuously monitors the operational state of the discharge FET and provides feedback control. By detecting whether the FET is in on-state or off-state and adjusting the gate control voltage accordingly, the system ensures rapid and reliable cutoff. The feedback mechanism allows the circuit to detect when cutoff is achieved and maintain the appropriate voltage state, preventing extended cutoff times caused by voltage division effects.
Solution Approach 2:
The gate control voltage parameter is dynamically changed based on operational requirements: a first voltage level (e.g., 0V) is used during normal operation to keep the FET on, and a second voltage level (e.g., negative voltage relative to source) is applied during shutdown to ensure rapid cutoff. This parameter change approach overcomes the voltage division problem by directly controlling the gate-source voltage difference, achieving fast and reliable cutoff without extended transition times.
Data Source
AI summary
A battery device includes a battery unit which has a plurality of batteries connected in series; first and second lines each led from a cathode and an anode of the battery unit; first and second semiconductor switch elements which are inserted into the first line; a driver configured to generate a drive signal to turn off one of the first and second semiconductor switch elements when a protective operation is performed; a third semiconductor switch element which is inserted between a gate of at least one of the first and second semiconductor switch elements and an intermediate voltage point of the battery unit; and a semiconductor switch controller including a detector configured to turn on the third semiconductor switch element when the drive signal is detected and to apply a potential smaller than a source potential to a gate of one of the first.