Hello, we are making a thesis where we use MOSFETs as an alternative radiation detector. So to explain it, it works when the mosfet is irradiated with an external radiation source; its voltage threshold increases, which will be used to determine the radiation dose. I’m currently asking for help on how we measure the voltage threshold. BTW, we are using an n-channel MOSFET (model: IRFP250NPbF). Also in the datasheet provided by the manufacturer, it says here VGS(th)/Gate Threshold Voltage Min: 2.0 ––– Max: 4.0 V. There is a condition here with VDS = VGS, ID = 250 A. Does this mean that to measure the VGS, we need to first satisfy the conditions? To measure the voltage threshold, what node will we use to measure the VGS (th)? Is it at the drain to the source terminal or still at the gate to the source terminal? Feel free to share your thoughts, if you have any. I would also like to add that we have already tried to supply a voltage at the gate with respect to the source terminal. We use a 4 V supply voltage, and when we tried to measure the VDS (drain to source voltage), there was a voltage drop, so we’ve got a 3.5 V. Also, we are using an Arduino to measure its voltage and a multimeter for checking.

  • Lazyhotodogu@lemmy.worldEnglish
    1·
    1 year ago

    I just want to ask some points:

    • Do you mean that to properly operate the LM334, we need to apply or reached the threshold voltage of the MOSFET which is around (2 and 4V)? But, i’ve tried to used it (LM334z) as a standalone and still it doesn’t work. maybe the LM334z is the problem hahaha *Regarding the resistor method, What do you think about the measured Vds, Vds=117mV (With an input current of 40uA)? i’m confused with the “how a change in Vds will affect the current” *Isn’t it Vds the parameter required for determining the dose? So if there is a constant current and resistance, how does the radiation affects the MOSFET? Will resistance or current increase upon irradiation leading to an increase in the measured Vds?
    • blarbasaurus@lemmy.worldEnglish
      1·
      1 year ago

      You will need to provide a voltage of at least the threshold voltage PLUS the minimum voltage of the LM334Z. If the LM334Z circuit by itself doesn’t work, that will be the first problem to figure out. Make sure you completely read through the datasheet https://www.ti.com/lit/ds/symlink/lm334.pdf?ts=1689139734046&ref_url=https%253A%252F%252Fwww.google.com%252F, there are example circuits in it for reference. For the resistor method, keep in mind that the current isn’t constant; the voltage is. Your current is dictated by your resistor and the voltage across it, which is the supply voltage minus the threshold voltage. If your threshold voltage changes as the dose increases (which is the typical behaviour), the voltage across the resistor will change, therefore your current will change, which will generate error in your reading. The only way to minimize this error is to apply a very high voltage (100’s to 1000’s of volts) to the resistor, such that a change in the threshold would become a rounding error.