UNIVERSITY of PENNSYLVANIA

DEPARTMENT OF ELECTRICAL ENGINEERING

Example of SPICE simulation of mutual inductances

The syntax for a mutual inductance is as follows:

Kname Inductor1 Inductor2 value_of_K

In which K is the value of the coupling coefficient that determine the mutal inductance: M=K.sqrt(L1xL2). An example of a complete SPICE file for the circuit given below follows.

(K=M/sqrt(L1xL2)=0.693)

Vin 1 0 sin(0 5 159.15 0 0)
Rs 1 3 100
Rl 4 0 500
L1 3 0 10M
L2 4 0 2M
K L1 L2 0.693
.TRAN 0.1M 10M
.PRINT TRAN V(3) V(4)
.PLOT TRAN V(3) V(4)
.END

Remarks:

1. SPICE always needs a reference node numbered 0. One can never leave any node floating. For that reason we have connected the two coils together to node 0 (or put a large resistor between it). As there is no current flowing through this section, the circuit will not change by connecting these nodes.

2. SPICE does not allow to connect a voltage source in parallel with an inductor, as it thinks that the voltage source is short circuited. You can place a small resistor (ex. 0.001 Ohm) in series with the voltage source to overcome this problem.

Jan Van der Spiegel;
jan@ee.upenn.edu
Created Sept. 30, 1995; Updated Feb. 8, 2007