AN957 Datasheet, PDF (1/13 Pages) List of Unclassifed Manufacturers – Measuring HEXFETCharacteristics

Index
Topics covered:
Measuring HEXFET^®Characteristics
(HEXFET is the trademark for International Rectifier Power MOSFETs)
• Converting the nomenclature from bipolars to MOSFETs
• P-Channel HEXFET Power MOSFETs
• Initial settings
• Breakdown
• Drain leakage
• Gate threshold
• Gate leakage
• Transconductance
• On-resistance
• Diode drop
• Characteristics in synchronous rectification
• Transfer characteristics
• Measurements without a curve tracer
• Device capacitances
• Switching times
• Gate charge
• Reverse recovery
• A fixture to speed-up testing time
• Related topics
AN-957 (v.Int)
1. General
Curve tracers have generally been designed for making measurements on bipolar transistors. While power MOSFETs can be
tested satisfactorily on most curve tracers, the controls of these instruments are generally labeled with reference to bipolar
transistors, and the procedure to follow in the case of MOSFETs is not immediately obvious. This application note describes
methods for measuring HEXFET Power MOSFET characteristics, both with a curve tracer and with special-purpose test circuits.
Testing HEXFET Power MOSFETs on a curve tracer is a simple matter, provided the broad correspondence between bipolar
transistor and HEXFET Power MOSFET features are borne in mind. Table 1 matches some features of HEXFET Power
MOSFETs with their bipolar counterparts. The HEXFET Power MOSFET used in all the examples is the IRF630. The control
settings given in the examples are those suitable for the IRF630. The user must modify these values appropriately when testing a
different device. The IRF630 was selected since it is a typical mid-range device with a voltage rating of 200 volts and a
continuous current rating of 9 amps (with T_C = 25°C). For measurements with currents above 20 amps, or for pulsed tests not
controlled by the gate, the Tektronix 176 Pulsed High
Current Fixture must be used instead of the standard test fixture.
The IRF630 is an N-channel device. For a P-channel device, all the test procedures are the same except that the position of the
Polarity Selector Switch must be reversed—that is, for P-channel devices, it must be in the PNP position.
The curve tracer used as an example in this application note is a Tektronix 576, since this instrument is in widespread use.
However, the principles involved apply equally well to other makes and models. Figure 1 shows the layout of the controls of the
Tektronix 576 curve tracer, with major controls identified by the names used in this application note. Throughout this application
note, when controls are referred to, the name of the control is printed in capitals. For all tests, when the power is on, the initial
state of the curve tracer is assumed to be as follows:
• LEFT/ RIGHT switch in “off” position
• VARIABLE COLLECTOR SUPPLY at zero
• DISPLAY not inverted
• DISPLAY OFFSET set at zero
• STEP/OFFSET POLARITY button OUT (not inverted)
• VERT/HORIZ DISPLAY MAGNIFIER set at NORM (OFF)
• The REP button of the STEP FAMILY selector should be IN
• The AID button of the OFFSET selector should be IN
To Order