National Instruments Over-Current Protection Circuit Design

National Instruments® is an Austin, Texas-based company that provides productivity tools for designing, prototyping and deploying systems for test, control and embedded design applications. With locations across the globe, including in Toronto, Canada, National Instruments® provides both students and professionals with world-class tools for circuit design. For marketing purposes, the NI branch in Toronto created a PID controlled H-bridge Brushed DC motor as a demonstrative design. This project utilizes the rapid development methodology of Circuit Design Suite, as well as field-programmable gate arrays (FPGA) and real-time processor of the Single-board Reconfigurable Input/Output (sbRIO). However, situations like high current outrage may arise when switching the DC motor between different speeds and directions. In order to minimize the unexpected damage to the circuit and sustain the system with robustness and stability, an over-current protection (OCP) scheme was devised for the existing circuit design. After investigation, the OCP selection was narrowed down to the following choices: Fuses and breakers, resistor-based sensor, transistor-based sensor and Analog-to-digital converter (ADC).

Ying Zhi, a second year co-op student from the University of Waterloo, was assigned to find the most suitable over-current protection scheme and incorporate it into the existing circuit design schematic.

Figure 1 – The signal path of NI's DC motor design