# Understanding NI 6528 MOSFET-Based Current Limiting Circuitry

Updated Feb 1, 2019

• PXI-6528
• PCI-6528

## Issue Details

In the NI 6528 user guide and specifications , I see that the card has MOSFET-Based Current-Limiting Circuitry. What is the purpose of this circuitry on the card and how does it affect the input current I can provide to the card?

## Solution

The specifications for input current on the 6528 are as follows:
 5 V input 3 mA/channel max 60 V input 3 mA/channel max

The MOSFET-Based Current-Limiting Circuitry will adjust the input current based on the input voltage. Think of the current-limiting circuit as a resistor that can change its resistance. It will automatically detect the amount of current that should be flowing through and change its resistance accordingly. If the user is inputting 60 V, then the resistance is 30 KOhms, allowing 2 mA of current. If the input is 5 V, the resistance is 3.3 KOhms, allowing 1.5 mA. If the user is inputting 28 V, then the 6528 will draw somewhere between 1.5 and 2 mA of current.