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How to Connect Digital Outputs for Maximum Response Speed

Digital outputs require an appropriate load to achieve their maximum switching speed. Without a sufficient load, the output may appear slower or less responsive than expected.

When first connected to a high-resistance input, such as an oscilloscope, Gantner Instruments digital outputs may appear slow or unresponsive. This occurs because the output requires a load to properly pull the voltage down. With an appropriate load, switching frequencies of up to 10 kHz can be achieved.

For example, considering the specifications of the Q.bloxx XL D101 module:

Load capacity

>0.5 A

>0.1 A

<0.1 A

response time

10µs

100µs

1000µs

The outputs are specified for 30 VDC / 0.5 A, so the response time is fastest when operating near the upper end of the load capacity. The resulting load resistance determines how quickly the digital output can switch.

Wiring diagram from the datasheet:

How to add an external resistor when the digital input has high impedance:

Please note that at 30 V and 0.5 A, up to 15 W of power may be dissipated as heat. When using a pull-down resistor, all power flowing through the resistor is converted into heat. Therefore, the resistor must be properly rated to withstand the resulting thermal load.