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High Amplitude Arbitrary/Function Generator Simplifies Measurement in Automotive, Semiconductor, Scientific and Industrial Applications Application Note

Figure 2. H-bridge configuration of four MOSFETs in a DC-motor drive.

Figure 3. MOSFET schematic and equivalent circuit.

Measuring Switching Time on Power MOSFETs

Power MOSFETs are used in a variety of automotive motion control, power management, and climate control applications. They drive small motors, solenoids, anti-lock brake, electrical power steering and electronic stability program systems as well as ignitor circuits for H.I.D lamps. They are also a key component of integrated starter/alternators.

When used as a switch, the MOSFET's basic function is to control the drain current via the gate signal. In these applications, switching time is an important criteria consid- ered by circuit designers during the component selection. A MOSFET’s switching performance is determined by the time required to establish voltage changes across its internal capacitances (see Figure 3). Note that the gate-to-source voltage must first charge the MOSFET’s input capacitance to its characteristic threshold level before drain current conduction can start.

Figure 2 shows an example of MOSFETs used in an H-bridge topology to drive a DC motor. This configuration provides forward, reverse and braking functions.

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