<WORK 03>

Measuring dynamic parameters of MOSFET, BJT and IGBT

Input tasks

Measure times t_ON and t_OFF (switch-on and switch-off time), commensurate them with the level of input controlling signal.
Plot these dependences: t_ON=f(U_GEN), t_OFF=f(U_GEN) for each transistor.

Circuit's diagram

Schematic diagram

		tD	delay time
		tR	rise time
		tON	switch-on time
		tS	storage time
		tF	fall time
		tOFF	switch-off time

Definitions of turn-on and turn-off times and delays.

Measured components

1.	BJT	KUY12
2.	MOSFET	IRF740
3.	IGBT	GT20J101

Process of measurement

The value of current flowing into the gate from generator should be controlled by amplitude of output voltage. This value of current is not directly shown on oscilloscope, it must be count from the differential voltage measured on resistor 50 W (channels 2 - 3). For measuring turn-on and turn-off times use time-cursors, that can be found in oscilloscope's menu CURSOR. Falling and rising slopes of controlling signal are considered as short, that they can be omitted. When triggering on rising slope turn-on time will be measured, when triggering on falling slope turn-off time will be measured. Time distances should be measured according their definitions, don't forget 10% and 90% of the level. The value of the charge, given to the gate during turning-on and turning-off can be obtain from following equation:

For this purpose use the red curve marked "4".

Supplement information

The influence of negative gate current on the turning-off process of BJT. When negative gate current during turning-off appears, the BJT component can turn-off faster (shown as a dot curve).

Real waveforms of turning-on and off process for MOSFETs

Typical measured waveforms

Turning-on the MOSFET

Turning-off the MOSFET

Legend:1 – Voltage U_CE, U_DS, 2 – voltage of the generator, 3-controlling voltage U_BE, U_GS, 4-difference voltage between curves 2 and 3 representing charge needed to "feed" the gate.