NCV7708

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15

The Cauer networks generally have physical significance

and may be divided between nodes to separate thermal

behavior due to one portion of the network from another.

The Foster networks, though when sorted by time constant

(as above) bear a rough correlation with the Cauer networks,

are really only convenient mathematical models. Both

Foster and Cauer networks can be easily implemented using

circuit simulating tools, whereas Foster networks may be

more easily implemented using mathematical tools (for

instance, in a spreadsheet program), according to the

following formula:

R(t)

+

n

i

+1

t taui

Time constants are not simple RC products. Amplitudes

of mathematical solution are not the resistance values.

Each rung is exactly characterized by its RC−product

time constant; amplitudes are the resistances.

Figure 11. Grounded Capacitor Thermal Network (“Cauer” Ladder)

Ambient

(thermal ground)

Junction

Figure 12. Non−Grounded Capacitor Thermal Ladder (“Foster” Ladder)

Ambient

(thermal ground)

Junction