How can I test a MOSFET for drain-source on-resistance on my curve tracer?
Drain-Source On-Resistance - RDS(on)
What is drain-source on-resistance?
Drain-source on-resistance (RDS(on)) is the resistance between the drain and the source of a MOSFET when a specific gate-to-source voltage (VGS) is applied to bias the device to the on state. As the VGS increases, the on-resistance generally decreases. The measurement is made in the ohmic (i.e. linear) region of the device. Generally speaking, the lower the MOSFET on-resistance, the better.
One of the ways to trace this resistance is to use a curve tracer. On a curve tracer, the so called “Collector Supply” drives the drain while the “Step Generator” drives the gate. For step-by-step instructions on how to test a MOSFET for drain-source on-resistance using a curve tracer, see below. For instructions on how to use an oscilloscope or SMU to measure MOSFET on-resistance, see our “What is the drain-source on-resistance of a MOSFET?” FAQ.
What the display shows:
The display shows VDS on the horizontal axis, and the resulting ID on the vertical axis. The specification is met when at the specified VDS, VDS/ID is less than or equal to the specified maximum.
How to test a MOSFET for drain-source on-resistance on a curve tracer:
1. Under Controls, set:
A:Max Peak Volts to the lowest setting above the specified VDS
B: Max Peak Power Watts to the lowest setting that satisfies (ID x VDS)
C: Collector Supply Polarity to (+DC) for N-channel or (-DC) for P-channel
D: Horizontal Volts/Div to display VDS between the 5th and 10th horizontal divisions
E: Vertical Current/Div to display ID between the 5th and 10th vertical divisions
F: Number of steps to minimum (zero)
G: Step Generator to Voltage
H: Step Generator Polarity to apply forward bias (+ for N-channel),
(- for P-channel)
I: Step/Offset Ampl to approx 50% of the specified VGS
J: Pulse to Long
K: Configuration to (Base/Step Gen, Emitter/Common)
L: Variable Collector Supply to minimum % (full ccw)
M: DotCursor ON
2. Apply power to the MOSFET:
A: Position the Left/Right switch as appropriate
B: Slowly increase the Variable Collector Supply until the specified VDS is reached
3. Compare to data sheet specifications:
A: Check that VDS/ID is less than or equal to the specified minimum
Tektronix Curve Tracers are discontinued products. More efficient and accurate methodologies and solutions have been designed to support curve tracing functionality on a much more compact form factor. One such solution is based on using a dual channel SMU or two single channel SMUs and software to control the bias voltage step generation and the relative drain to source voltage drop. To learn more, see our “What is the drain-source on-resistance of a MOSFET?” FAQ.
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