Diode Parameters - Which ones matter for a High Voltage Multiplier?

Discussion in 'The Projects Forum' started by Ravi72, Jul 15, 2016.

  1. Ravi72

    Thread Starter New Member

    May 31, 2016
    I have 3 questions, but first, to give you some background, I am designing a High Voltage Multiplier (I am using LTSpice) and I use the (two-diodes, two-capacitors per stage) set up and go from 12kV to about 480kV on the output, over a total of 20 stages. So the model contains about 40 or 80 identical diodes, depending on their rating. I am also interested in meeting stringent ripple requirements on the output.

    As you can tell, it is important that diode parameters that have a strong impact upon the final current/voltage and the operational feasibility of a selected commercial diode model are fully understood. I have been running a number of studies, looking at the impact of the variance of each parameter of the diode D, upon the circuit.

    For instance Is, Tt, Vj are all super important.

    Q1: Could someone clarify for me, how to effectively use the emission coefficient of a diode? This is the parameter 'N' listed above, in the 'D Diode' LTWiki. Commercial diodes I am looking into do not give any info. on the 'N' of their specific model. I understand the number must be between 1 & 2. An inherited model I am using as a guide used an N of 62, which seems absurd, but the program does compile, so what in world? And how do I determine one for the models I am considering? The manufacturers themselves either do not know or won't tell.

    Q2: The Rs, Ohmic resistance... I fished around LTWiki and it seems as though it is not too important if I am carefully limiting my circuit's currents to below the large levels at which it becomes resistance. For instance, if my diode has a max. avg. forward current of 20 mA, and my circuit limits the current to no more than say 50 or 60 mA, then I can safely ignore the Rs value and leave it at its default value, right? Or?

    Q3: Fc Coefficient for Forward-Bias depletion capacitance? Leave it at default? Again, the manufacturers are unable or unwilling to give any such data.

    Am I missing important stuff?
    Please and thank you for useful information/clarification/edification on this!
    Its very important to me to get this right and lots riding on it.

  2. Bordodynov

    Well-Known Member

    May 20, 2015
    Really high voltage diodes consist of a plurality of diodes connected in series. single diode breakdown voltage of 400-800 V. Therefore, a large value of "n" adequately reflects the characteristics of the diode.