USB 6008 Digital outputs volt and current

[Mr.Engineer]

Hello,

I use 10 V 500 mA power supply to source the USB-6008 MultiFunction Board. ( the power supply is directly connected to the last 2 pins of DAQ). Now , i am connecting a solid state realy which draw 18 mA and takes 9 V to P0.0 . it works fine but i wonder how long it will work? Is it an overload. What is the benfit of using an external power supply and do not daw the current from PC?

I have observed that the output volt of the digital outputs is almost equal to the input volt of power supply. can i continue working with this volt and current(9V 18mA)? and why ? Thanks

Samer

[Dennis_Knutson · Accepted solution]

I can't imagine that connecting an external power supply would help the device. The +5 line is an output - designed to power external devices and not as an input. You are probably stressing a lot of different parts that are designed to work at 5 volts and a certain current. You should really be using an external circuit that accepts 5 volt inputs and amplifies the voltage and current to levels you need to drive the relay. Connect the external power supply to this circuit. It's probably to late to avoid voiding the warranty but maybe it is not to late to avoid a complete failure of the 6008. Hopefully, someone from NI that is familiar with the 6008's circuitry will post saying that no damage has been done.

[S_Hong]

Hi Mr. Engineer,

Unfortunately, the USB-6008/9 was not designed to take in a external power supply to drive the DIO lines to a different rail, therefore, although the internal circuitry may result in a higher DIO output, you are in fact exceeding the specifications of the USB micro controller for the DIO. So although this might work for a while, it may also be damaging the hardware and therefore we cannot recommend this solution. If you would like to provide a higher rail for your relay, I would suggest using external components to build a level shifter for your application.

I hope this helps answer your question.