IV Curve

An I_D over V_DS plot can be directly extracted from plotting I_D over V_GS for multiple values of V_DS. This is done under hard switching conditions with an inductive load, as it is present in a double pulse test. The transistor should be switched very slowly and therefore a large gate resistance should be used. The turn-on and turn-off I_D-V_GS curves look different. This is among other factors due to the common source inductance L_S in the transistor and the abrupt change of I_D over time. The two values for the measured gate voltage can be described as    with:

• v_{gs_on}and v_{gs_off}: measured gate voltage during turn-on and turn-off
• Δt_r, Δt_f: rise and fall time of the drain current
• v_i: real gate voltage
• L_S: common source inductance
• ΔI_d: switching drain current

With this, the real gate voltage can be calculated as:     for each output current and output voltage value. These values can then be transferred to an I_D-V_DS plot for different values of V_gs.This method can also be applied to IGBTs.

PD1000A software samples I_D over V_g during turn-on and turn-off at a certain voltage V_DS during turn-on and turn-off and creates the weighted waveform for the real gate voltage. Afterwards values of this graph at certain values for V_g are used to plot points in a I_D-V_DS plot. With a V_DS-sweep the whole IV characteristics can be plotted.

 

Waveform example of sampling I_d over V_g

 

Waveforms showing difference between turn-on and turn-off

 

Graph with I_d-V_g waveforms for multiple V_d

 

Currently PD1000A software only starts at a gate voltage of 0 V. This is not sufficient to extract the IV-curves for depletion mode transistors. There is only a minor adaption necessary, this is starting the sampling process already for negative values of V_g. Also, Vg/Id sampling seems to be not working properly as sometimes waveforms seem to be incomplete.