# How can I test a MOSFET for Drain-Source On-Resistance on my curve tracer?

### 問題：

How can I test a MOSFET for Drain-Source On-Resistance on my curve tracer?

### 答案：

Drain-Source On-Resistance - RDS(on)

What It Is:

Drain-source on-resistance is the resistance between drain and source with a specified VGS applied to bias the device to the on-state.  The measurement is made in the ohmic (i.e. linear) region of the device.

On the curve tracer the Collector Supply drives the drain and the Step Generator drives the gate.

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 Do It:

1. Set controls:

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