Tactile Drive Circuit With Switched Feedback for Clean FET Turn-Off
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Solution Overview
Problem
Current drive circuits using operational amplifiers on the low side of a load fail to efficiently turn off the field effect transistor (FET) due to offset voltage and high gain, leading to inefficient driving of loads, particularly in tactile sensation generators.
Innovation Solution
A drive circuit design that includes a first switching element in the current path connecting a load with a resonance frequency to a reference potential, a drive element with input terminals for load and control signals, and a second switching element in a connection path to control the operational amplifier's gain, allowing for efficient driving by switching the FET on and off to simulate an ideal sinusoidal waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an operational amplifier is used to drive a FET on the low side of a load, then the circuit can provide high gain amplification, but the offset voltage and high gain cause the FET to fail turning off completely, reducing driving efficiency
Solution Approach 1:
The patent extracts the problematic offset voltage effect from the operational amplifier's output by introducing a second switching element that actively disconnects the feedback path during the FET off-state. This separates the amplification function (when needed) from the off-state control function, preventing the offset voltage from affecting the FET's off-state reliability while preserving driving efficiency during the on-state.
2Power
If the operational amplifier maintains high gain during the FET off-state, then it can amplify control signals effectively, but it amplifies minute offset voltages that prevent the FET from turning off
Solution Approach 1:
The patent applies periodic action by using the second switching element to periodically connect and disconnect the feedback path in synchronization with the FET's on/off cycles. During the FET on-state, the feedback path is connected to provide high gain amplification for effective signal amplification. During the FET off-state, the feedback path is disconnected to prevent amplification of offset voltages, thus eliminating the harmful effect while preserving the beneficial amplification capability when needed.
Data Source
AI summary
A drive circuit includes a first switching element inserted in a current path connecting a load with a resonance frequency to a reference potential point, a drive element having a first input terminal to which a load signal obtained by converting a current flowing in the current path into a voltage is input, a second input terminal to which a first control signal that serves as a reference for operation of the first switching element is input, and an output terminal connected to a control terminal of the first switching element, and a second switching element inserted in a first connection path connecting the output terminal of the drive element and the first input terminal of the drive element.