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Operation Overview 17
operation, protection features, and other operating features of the Electronic Load.
Extended Power Operation
Note: Extended power operation is not available on "B " load modules (Agilent Models 60501B-60507B).
In addition, this feature may not be present in "A" modules produced after 1989.
The extended power feature allows a module to dissipate considerably more than its nominal power rating in many cases.
The primary factor limiting the amount of power that can be dissipated is the temperature of the current-control pass
transistors, as sensed at the heatsink. A module’s nominal power rating is specified for continuous power at high ambient
temperature, but in many applications average power is less than 100%, and ambient temperature is considerably lower than
the highest specified full-power temperature. In these less-than-extreme applications, each load module can safely dissipate
as much as one third more power than its nominal power rating for a limited time.
In effect, each module has two power-limit curves, as shown in Figure 2-1. Whether the module is operating with the
nominal power-limit curve or the extended power-limit curve is determined by heatsink temperature. The module turns on
with extended power available and extended power continues to be available unless and until the internal temperature rises
beyond a safe operating point for extended power. At the point, the module automatically reduces the power-limit curve to
the module’s nominal power rating, and sets the Extended Power Unavailable (EPU) bit in the status registers. Extended
power is available any time the EPU bit (bit 9) is not set. A graph provided in the module-specific specifications under DC
Input Rating shows the typical time that a module can operate at full extended power after having stabilized at a given
average power before extended power becomes unavailable.
Figure 2-1. Power Limit Curves
Programmable Features
Modes of Operation
The three modes of operation are:
• constant current (CC)
• constant voltage (CV)
• constant resistance (CR)