AN957 Datasheet, PDF (6/13 Pages) List of Unclassifed Manufacturers – Measuring HEXFETCharacteristics

Index
AN-957 (v.Int)
11.The device is connected using the LEFT/RIGHT switch. Increase the VARIABLE COLLECTOR SUPPLY voltage until rated
current is reached (9A for the IRF630). Read V_SD from the trace (see Figure 9).
9. Composite Characteristics
The forward and reverse characteristics of the HEXFET Power MOSFET may be viewed at the same time. This display can be
used to obtain an appreciation of the HEXFET Power MOSFET’s behavior in applications in which current flows in the channel
in either direction. such as synchronous rectifiers and analog waveform switching. The procedure is the same as for on-resistance
except that:
1. OFFSET is set to zero.
2. The POLARITY control is set at "AC".
3. The device is connected using the LEFT/RlGHTswitch. The VARIABLE COLLECTOR SUPPLY voltage is increased to
obtain the required peak value of I_D. Beware of device heating. Figure 10 shows the trace obtained with the IRF630. To obtain
the reverse characteristics of the diode alone, invert the step polarity. The FET is inoperative, and the display will resemble
that shown in Figure 11. The step polarity should also be inverted to obtain the composite characteristics of P-channel
devices.
PER
V
2
E
R
T
A
DIV
200 PER
H
O
R
Z
mV
DIV
PER
V
2
E
R
T
A
DIV
200 PER
H
O
R
Z
mV
DIV
Figure 10. Operation in first and third
quadrant (synchronous rectification)
Figure 11. Operation in first and third
quadrant without gate drive
10. Transfer Characteristics
The transfer characteristic curve of I_D versus V_GS may be displayed using
the pulse mode. The test is set up in the same manner as the on-
resistance test, except for the following:
1. OFFSET MULTIPLY should be set at zero.
2. Set HORIZONTAL VOLTS/DIV on “STEP GEN”.
3. The 300 microsec button of the PULSED STEP SELECTOR should
be IN.
4. Increase the VARIABLE COLLECTOR SUPPLY voltage to obtain
the trace shown in Figure 12. The transfer characteristic is outlined
by the displayed points.
PER
V
1
E
R
T
A
DIV
PER
H
O
R
Z
DIV
Figure 12. Transfer characteristic (I_D vs V_gs)
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