Straight Facts about Linear
MOSFETs and their Applications
Linear-mode applications such as class-A audio amplifiers, active DC-link discharge, battery
charge-discharge, inrush current limiter, low-voltage DC motor control or electronic loads demand
the power MOSFETs to be operated within the current saturation region. Standard MOSFETs are
prone to ETI when used in linear-mode applications leading to possible device destruction. Linear
MOSFETs are the most appropriate choice for linear-mode applications to ensure reliable operation.
José Padilla, Director Product Marketing; Aalok Bhatt, Product Marketing Engineer;
Vladimir Tsukanov, Senior Principal R&D, Littelfuse
Introduction – What is linear-mode operation and why is it
required
Power MOSFET’s output characteristic can be divided in to three
distinct regions namely ohmic region, non-linear region, and saturation
or active region as displayed in Figure 1. In the ohmic region,
the drain current ID is directly proportional to the drain-source voltage
VDS for a given gate-source voltage VGS. The MOSFET acts as a
resistor in this operation mode with a value equal to its on-state resistance
RDS(ON). In the non-linear region, the MOSFET’s resistance
behaves non-linearly and the rate of increase of ID with VDS slows
down. In the active region, the MOSFET’s channel is saturated with
majority charge carriers. In this region, ID is independent of VDS.
ID is governed only by VGS and it remains constant for any given
VDS. In other words, the MOSFET exhibits the behavior of a constant
current sink. This operating mode is commonly known as linear operation
mode of power MOSFETs. In this operating mode, the MOSFETs
typically dissipate higher power levels than they would in the
more common switched-mode applications due to simultaneous
occurrence of high voltage and current[1].
VIEW FULL TEXT: MAGAZINE BODO POWER SYSTEM -OCTOBER 2021
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