Negative Rail Current Driver for Torque Motor Power Balance
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Solution Overview
Problem
Existing linear voltage controlled current drivers for torque motors typically draw power only from a positive voltage rail, leading to an imbalance between the power supplied by the positive and negative voltage rails, especially when multiple torque motors are used, requiring complex control circuitry adjustments or level shifters to accommodate a negative voltage rail.
Innovation Solution
A current drive circuit that supplies controlled current to inductive loads from a negative voltage power supply, allowing the use of a positive voltage input signal to determine the current magnitude, thereby balancing power draw between the positive and negative voltage rails without altering the control circuitry or adding level shifters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If current drivers are powered only from a positive voltage rail, then the control circuitry remains simple, but the power distribution becomes unbalanced between positive and negative rails
Solution Approach 1:
The patent inverts the conventional approach by powering the current driver from the negative voltage rail instead of the positive voltage rail. This allows the driver to source current to the load while sinking return current to ground, balancing the power distribution. The driver circuit uses an N-channel MOSFET whose source connects to the negative rail, enabling it to operate with the negative supply while maintaining simple control circuitry that accepts positive voltage control signals.
2Device complexity
If multiple torque motors are used with positive rail only, then control is simplified, but the positive voltage rail carries excessive current creating noise and requiring larger conductors
Solution Approach 1:
The patent segments the power distribution by dividing the torque motor fleet into two groups: some motors are powered from the positive voltage rail while others are powered from the negative voltage rail. This segmentation balances the current load between the two rails, reducing electromagnetic noise and allowing the use of smaller, less expensive conductors. Each current driver independently controls its motor using simple control circuitry that works with either power configuration.
Data Source
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Figure 2A
AI summary
A method and current drive circuit are provided that accepts a positive voltage input signal and supplies power to a load (110d-f) from a negative voltage rail.