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REF200 current source

Karthik R
Prodigy 240 points
Other Parts Discussed in Thread: REF200, PGA204, LMP90100

Hi,

We are developing a cryogenic temperature controller, and we are using Lakshore's Silicon diode sensor  for temperature measurement, this diode sensor takes a four wire configuration, as shown in below fig-1 , and it requires a excitation current of 10μA , we are using REF200 for generating the required excitation current, the circuit used is also shown below, i'm getting I+ from the Iout of the circuit shown below in fig-2, i have a small question ,can i connect the I- terminal of the diode to gnd or i should have similar setup which gives me I-, Pls help me in clearing this silly doubt . Further for obtaining the voltage from the diode sensor we need to have a high impedance voltage measurement source like voltmeter etc., for this measurement we are using PGA204 an instrumentational amplifier which is shown below in fig-4, Pls suggest the best way to measure the voltage or can we proceed with the PGA. Pls help me clearing these doubts. Looking forward for positive and speedy reply .

Thanking you

Karthik.R

              Fig-1                                                      

Fig-2

  Fig-3

                                 

                                                      Fig-4

 

  • 0
    Guru 21975 points

    Karthik,

    The I- terminal of the diode can be connected directly to ground. The two inputs of the PGA204 should be connected to the V- and V+ terminals of the diode.

    The PGA204 and OPA128 will require a dual +/- power supply as discussed in the data sheet for this device. For a 10uA output current, you could use a general purpose FET-input op amp instead of the OPA128.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 240 points

    HI,

    Thank you Bruce trump for your speedy reply, it was suggested in the application note to use OPA128, so just followed it, and i wanted to know the voltage ( +Vs, -Vs ) that we have give for REF200 .

    Thanking you

  • 0 in reply to Karthik R
    Prodigy 240 points

    Hi, 

    There is a small doubt , can i use LMP90100 instead of PGA204 and ADC in later stages of circuit design, so that it will reduce the power consumption as well as space.

    Thanking you 

  • 0 in reply to Karthik R
    Guru 21975 points

    Karthik,

    I am not familiar with the LMP90100 but it looks well suited to the measurement.

    The REF200 only needs two connections. One to the op amp's inverting input and the other to the -15V supply.

    Regards, Bruce.