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Differences Between Line Driver, Open Collector, and Push Pull Encoders

Updated Jan 9, 2019

Issue Details

I want to determine the difference between line driver, open collector, and push-pull quadrature encoders and how to tell which type I should use.

Solution

Line Driver
A line driver is a sourcing output. When in the on state, a line driver will supply Vcc. In the off state, a line driver will float. Because of this, a sinking input is required for proper operation. Please refer to the table below for a simple example of a line driver.

Open Collector
An open collector is a sinking output. In the on state, an open collector will supply a path to ground. When in the off state, an open collector will float. For proper operation, a sourcing input is required. Please refer to the table below for a simple example of an open collector.

Push-Pull
A push-pull output is a combination of a line driver and an open collector. In the off state it will supply a path to ground and in the on state it will supply Vcc. Please refer to the table below for a simple example of a push-pull output.


For most NI DAQ cards, a Push-Pull quadrature encoder is recommended, because the Multifunction DAQ card works best when it is constantly driven. As mentioned above, the Push-Pull configuration does not float, it is always supplying Vcc or ground, which is why it will work best with a Multifunction DAQ card.

If you are working with an Industrial I/O Card, check the user manual for the best quadrature encoder type.

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