NMOSFET Gate Pre-Charge for Faster Switch Turn-On
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Solution Overview
Problem
The response time required for a NMOSFET switch to turn on, due to the need for the gate voltage to rise from zero to a threshold, degrades the switching speed and operation speed of power supply circuits.
Innovation Solution
A quick turn on apparatus and method that maintains the gate voltage of the NMOSFET switch at a non-zero level just below the threshold, using a combination of switches, diodes, and charge pumps to speed up the turn-on process by eliminating the need for the gate voltage to rise from zero, thereby reducing the time required for the switch to turn on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the gate voltage is pulled high from zero to turn on the NMOSFET switch, then the switch can be turned on, but the response time is degraded and switching speed is reduced
Solution Approach 1:
The patent applies preliminary action by pre-charging the gate voltage to a non-zero level (specifically to a voltage level that is below the threshold voltage but above zero) before the actual turn-on is needed. This is achieved through a pre-charge circuit that charges the gate capacitor to a predetermined voltage level during the off-state. When turn-on is required, the gate voltage only needs to be increased from this pre-charged level to the threshold voltage, significantly reducing the charging time and improving switching speed while minimizing the time loss.
2Speed
If the gate voltage is maintained at a non-zero level to speed up turn-on, then the switching speed is improved, but the gate voltage must be carefully controlled to prevent unintended turn-on
Solution Approach 1:
The patent applies parameter changes by carefully selecting and controlling the gate voltage level during the pre-charge state. The gate voltage is maintained at a specific voltage level that is above zero (to enable fast turn-on) but strictly below the threshold voltage (to prevent unintended turn-on). This precise parameter control allows the switch to be prepared for rapid activation while maintaining reliable control and preventing false triggering. The pre-charge voltage level is designed to be optimally positioned in the sub-threshold region.
Data Source
AI summary
A quick turn on apparatus and method for a NMOSFET switch are used to maintain the gate voltage of the NMOSFET switch non-zero but not enough to turn on the NMOSFET switch, such that the NMOSFET switch turns on more quickly when it is to be turned on. Seamless transition can be further achieved in a single pole double throw switching circuit by using the quick turn on apparatus and method.