Brushed DC Motor H-Bridge Control PCB Rapid Prototyping using NI Ultiboard

1. Introduction

NI offers a complete design solution that helps engineers in many application areas from power electronics, to automotive, to clean energy in:

1. Accurately simulating their system at a desktop level whether being an analog circuit, an FPGA code, or an embedded control system of both analog digital components including all system dynamics
2. Rapidly prototyping and deploying the design using modular embedded hardware platforms such as Compact RIO and Single Board RIO as well as the Ultiboard PCB design tool for custom board designs. Typically, Ultiboard is a powerful tool for rapid prototyping of custom boards for the reconfigurable embedded control and acquisition system of Compact RIO that includes I/O modules, a reconfigurable field-programmable gate array (FPGA) chassis, and an embedded controller as well as for Single Board RIO which combines deployable, embedded devices that feature a real-time processor, reconfigurable field-programmable gate array (FPGA), and analog and digital I/O on a single board programmed with NI LabVIEW software.

A DC motor H-bridge control circuit can be simulated in Multisim and LabVIEW using closed-loop analog and digital co-simulation, where Multisim’s SPICE engine simulated the analog circuitry of the MOSFET switches and the DC motor model while LabVIEW was used to simulate the control logic for the switching (including FPGA) as explained in this link.

The prototyping stage includes the deployment of the control code on Compact RIO and the prototyping of the PCB that includes all the electronic components using Ultiboard. 

In this tutorial, the steps of translating the Multisim design into a PCB design are explained which has been fabricated by NI's partner, Sunstone Circuits, while the complete project page is available in the Desigcon 2012 publication here.

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2. The Multisim Schematic Capture

The Multisim design consists of a full H-bridge circuit that controls the speed of the motor by enabling one of the two switches diagonal arms at a time (U3 and U6, or U4 and U5) using the control signals coming from Compact RIO (NI-9401 DIO-4 to DIO-7).

The high current output stage of the MOSFETs is connected to the DC motor in series with a current sensor, while the output current is fed back to the Compact RIO input module NI-9227 and the modulated speed data (Channels A,B, and I the NI-9401 DIO-0 to DIO-2)

Below is a png snippet of the schematic capture, simply expand the image to drag and drop it in Multisim and the design will load.

Figure 1: Schematic capture of the H-bridge circuit

The connectors used in this design are:

1. -      Standard DB-25 for the compact RIO connection
2. -      Molex 8981 4-pin connector for the power supply (footprint created)
3. -      Standard 100mil-pitch pin headers for the motor and the speed sensor

One of Multisim's advantages is that it includes a database of over 200 connector symbols and footprints for NI hardware and other industry standard connectors. In the Multisim database, under the NI_Components family, you can find a whole set of connectors for NI DAQ, NI SCXI, NI Single Board RIO, and NI Compact RIO

Figure 2: NI Connectors in Multisim's database

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3. The Ultiboard design

Part Placement and Board Preparation

The first step is to automatically transfer the schematic capture from Multisim to Ultiboard by clicking in the Multisim menu on Transfer>Transfer to Ultiboard>Transfer to Ultiboard 12.0

The following image shows the transferred design in Ultiboard

Figure 3: Unplaced parts of the design in Ultiboard

To place the components on the board, the part sequencer in the spread sheet view is used instead of the automatic placement to have a specific layout that preserves the shape of the H-bridge and for the connectors to be on the edge of the board. Once all the parts are placed, the board outline is adjusted to a smaller size.

For the connector J3 and the heat-sinks, the footprints did not exist in the Ultiboard database; therefore custom footprints have been created for them following these steps:

1. Go to Tools>Database>Database Manager and under the User Database, click on Create New Part under the Parts section to create a new footprint.

Figure 4: Ultiboard's footprints datbaase

1. Create the shape of the silkscreen and the pads based on the datasheets of the heat-sinks and the connector.
2. Once the shape is drawn, click on File>Save to Database to be able to use it your design.
3. Go to your design, select the J3 power supply connector then click on Tools>Replace Part and select the new footprint
4. Go to Place>From Database and select the heat-sinks to be placed in front of the MOSFETs

The following image shows the layout with the placed parts

Figure 5: Ready-for-routing board

The board settings are defined under Options>PCB Properties with 2 layer pairs. The first layer is defined as a power plane for the +12V node, while the second inner layer is used as a power plane for the ground connection by going to Place>Power Plane in the Ultiboard menu.

Figure 6: Copper layer settings in Ultiboard under the PCB Properties

Board Routing and Finalization

The current rating of this board is 20 Amperes, which means that the traces should be thick enough to sustain this current without an increase in temperature that might harm the electronic components. The traces carrying high current were set to a width of 400 mils and where routed on the top copper layer, while the rest of the traces where ranging between 20 and 50 mils.

Finally, text has been added to the board indicating the application of the design.

Figure 7: Finalized layout in Ultiboard

At this point, the design is ready for fabrication and a 3D preview is generated to confirm the board looks as desired simply by clicking on Tools>3D View

Figure 8: 3D Preview of the design in Ultiboard

Finally, the Gerber files were exported and sent for fabrication to NI’s partner Sunstone Circuits. The integration between Ultiboard and Sunstone’s process is standardized and verified guaranteeing high quality board fabrication.

Figure 9: Fabricated Board by

Figure 10: Brushed DC motor control system with Compact RIO and the Ultiboard prototype

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4. Additional Resources

• Custom Circuit Design for NI Hardware
• Implementation of a DC-Motor H-Bridge Circuit and Control Logic Using Multisim and LabVIEW FPGA
• Analog and Digital Closed-Loop Co-Simulation With LabVIEW
• Getting Started with NI Ultiboard