A A PPLICATION PPLICATION N N OTE OTE
AN-936
International Rectifier • 233 Kansas Street, El Segundo, CA 90245 USA
The Do’s and Don’ts of Using MOS-Gated Transistors
In this application note, some of the most common do’s and don’ts of using HEXFET
® power MOSFETs are described.The objective is to help the user get the most out of these remarkable devices, while reducing “on the job” learning timeto a minimum.
1. Be Mindful of The Reverse Blocking Characteristics of The Device
IGBTs have a limited reverse blocking capability of approximately
20-30 V, with high leakage. This is characterized in IR’s data
sheets with a Reverse Avalanche Energy (E
ARV ). This rating isuseful to absorb energy spikes due to the stray inductance in series
with the anti-parallel diode. This is a significant advantage over
bipolar
transistors and power darlingtons. A feature of power
MOSFETs is that they inherently have built into them an integral
reverse body-drain diode. The existence of this diode is explained
by reference to Figure 1. When the source terminal is made
positive with respect to the drain, current can flow through the
middle of the source cell, across a forward biased P-N junction. Inthe “reverse” direction, the HEXFET
® power MOSFET thusbehaves like a P-N junction rectifier. The integral body-drain diodeis a real circuit element, and its current handling capability is
typically as high as that of the
transistor itself. Some circuits
require an “inverse” rectifier to be connected across the switching
device, and in these circuits it will often be possible to utilize the
body-drain diode of the HEXFET power MOSFET provided the proper precautions are taken. • • Devices should be handled by the package, not by the leads. When checking the electrical characteristics of the MOS-gated
transistors on a curve tracer, or in a test circuit, the following precautions should be observed: Test stations should use electrically conductive floor and table mats that are grounded. Suitable mats are availablecommercially. Figure 1. Basic HEXFET MOSFET Structure • MOS-gated
transistors should be left in their anti-static shipping bags, or conductive foam, or they should be placedin metal containers or conductive tote bins, until required for testing or connection into a circuit. The person handling
the device should ideally be grounded through a suitable wrist strap, though in reality this added precaution is seldom
essential.
2. Be Careful When Handling & Testing HEXFET
®
Power MOSFETs
The user’s first “contact” with a MOS-gated
transistor could be a package of parts arriving on his desk. Even at this
stage, it behooves one to be knowledgeable about some elementary precautions. Being MOS devices, HEXFET power
MOSFETs can be damaged by static charge when handling, testing or installing into a circuit. Power Devices have large
input capacitance, and are able to absorb static charge without excessive buildup of voltage. In order to avoid possible
problems, however, the following procedures should be followed as a matter of good practice, wherever possible: HEXFET
® is the registered trademark for International Rectifier Power MOSFETs www.irf.com 1
