User Guide

Control system parts
171
An instantaneous device example: modeling a
triode
This section provides an example of using various ABM
parts to model a triode vacuum tube. The schematic of the
triode subcircuit is shown in Figure 47.
Figure 47 Triode circuit.
Assumptions: In its main operating region, the triode’s
current is proportional to the 3/2 power of a linear
combination of the grid and anode voltages:
ianode = k
0
*(v
g
+ k
1
*va)
1.5
For a typical triode, k
0
= 200e-6 and k
1
= 0.12.
Looking at the upper left-hand portion of the schematic,
notice the a general-purpose ABM part used to take the
input voltages from anode, grid, and cathode. Assume the
following associations:
•
V(anode) is associated with V(%IN1)
•
V(grid) is associated with V(%IN2)
•
V(cathode) is associated with V(%IN3)
The expression property EXP1 then represents V(grid,
cathode) and the expression property EXP2 represents
0.12[V(anode, cathode)]. When the template substitution
is performed, the resulting VALUE is equivalent to the
following:
V = V(grid, cathode) + 0.12*V(anode, cathode)
Pspug.book Page 171 Wednesday, November 11, 1998 1:14 PM