Output Capacitance Selection
A switchable output capacitor can be enabled on channel 1 of the NI PXI-4130 to help the device operate normally under unstable conditions. Enabling this output capacitor can also be useful in filtering ripple in higher current ranges. Use the niDCPower Output Capacitance property or the NIDCPOWER_ATTR_OUTPUT_CAPACITANCE attribute to enable or disable the capacitor.
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Note Changing the output capacitance requires channel 1 to be disabled, and may cause a glitch in the device output. |
| Output Capacitance Setting | Output Capacitance |
|---|---|
| Low | 10 nF |
| High | 6.8 μF |
Instability in the SMU Output on Low Capacitance Setting
When using the SMU with the Low Capacitance setting, the combination of output currents 200 mA and above, inductive loads greater than 2 μH, and resistances below 1 Ω can induce instabilities in the device output. The following list includes examples where these instabilities may be found:
- Driving current sense or power resistors
- Wirewound loads
- Transformers
- Shorted leads greater than 15 cm
- Any of the above combined with remote sense
In these cases, using the High Capacitance setting dramatically reduces the chances of observing resonance or oscillations between the SMU and the load. Alternatively, you can provide an external capacitance at the load. NI recommends starting with a capacitance of at least 0.1 μF. More than 10 μF should not be necessary, but can be used if required.
Remember that large capacitances (>0.1 μF) result in a slower output response. Refer to Load Considerations for more information about capacitive loads.