How do the turning-off times (tS, tF and tRR)
depend
on the value of decreasing current slope di/dt.
Confirm the equation
URRM=UK(1+tS/tF)
Circuit's diagram
Process of measurement
The forward current IF flowing through the diode decreases to zero
when the diode comes from the forward to the reverse biased. According to
diode's characteristic and when ignoring
the leakage current, reverse biased diode doesn't exhibit reverse current until the reverse
voltage exceeds breakdown voltage. However, in practice the power diode exhibits
reverse current for a short time due to the free charge-carriers.
These minority charge-carriers require some finite time (reverse recovery time) to recombine with
opposite charge-carriers in order to be neutralized. This time is called the reverse recovery
time and is defined on the next figure.
tRR = reverse recovery time, defined as the time difference between the initial zero crossing of the
diode's current and the time when this current reaches 25% of the peak reverse current. IRRM = maximum reverse current tS = time difference between zero crossing of IF and the maximum
of reverse current. This time is caused by the
charge stored in the depletion layer of the junction. tF = time difference between maximum of reverse current IRRM and 25% of the
maximum
reverse current IRRM. This time is caused by the charge stored in the bulk semiconductor material.
Setting of oscilloscope
Triggering: source CH1, falling slope, mode edge
Time: 5 us/div
CH1: 50 mV/div
CH2: 5 V/div
Probe's setting
Voltage: 1:100
Current: MTC 2,5 kA/1 V
Caution: High voltage can appear in the plexiglas-box, don't open the cover
when measuring!
