APPLICATION NOTE
5
Figure 7: Constant Power Load using table
In power systems, it is common to encounter loads which draw constant power. To model such a load, we
can use a voltage dependent current source. A first approximation looks like this:
gload A B value = {pload/v(A,B)}
Where A and B represents the positive and negative terminal nodes of V1.
With this formula, the power = v*i = v(A,B)*(pload/v(A,B)) = pload, as desired.
Unfortunately, this first approximation behaves badly near v = 0. When calculating the bias point for
more difficult circuits, PSpice reduces the power supplies. PSpice relies on the assumption that, when the
supplies are close enough to 0, all devices in the circuit are turned off. The above formula violates this
assumption. Further, it is not a good model of a real constant-power load for low voltages.
Figure 8: Constant Power Load
