26
Thermal Characteristics
The amplifiers are specified to operate at a 45° C ambient. This is not a maximum safe
operating specification. There are no parts in the amplifier that can not operate at a 60° C
temperature. The absolute maximum temperatures that the amplifier can operate at are
determined by thermal switches on the bridge switch power devices (IGBT's) and on the shunt
loads. These thermal switches open and disable the amplifier at 85° C.
At temperatures above 45° C, the amplifiers ability to produce its continuous rating is impaired
by the heat rise from the ambient temperature, and the amplifier will thermally shut down once
the 85° condition is sensed at either the bridge or the shunt load.
A guideline for enclosures would be to assume that the amplifiers thermal losses are 1350
watts.
If the application is causing bus pumping, and the shunts are being used, the thermal rise from
the shunts is restricted to 85° C and the actual power rating of the shunt load. The thermal
rise could be 2700 watts if the motor is constantly being started and stopped.
The amplifiers can be supplied with different shunt loads as options, and in some instances it
is a requirement to mount the shunt loads external of the amplifier.
