VARISTOR MODEL
==============   

The varistor model basically consists of 4 elements:

	   O                    
	   |            The resistance R_SERIES is required for
           |            mathematical reasons and has the
           |            constant value of R_SERIES = 100 nOHM.
	 +-+-+ 
         |   |      
	 |   |
R_SERIES |   |          In accordance with the equivalent circuit the 
         |   |          elements L_SERIES and C_PAR represent
         |   |          the lead inductance L and the parallel capacitance C.
         +-+-+          The values of L and C differ from type to type and
           |            are defined as parameters in file SIOV.LIB.
           |
           |            
	   |             
	 +-+-+          
	 |XXX|          The "resistance" R_VAR describes the non-linear
	 |XXX|          characteristic of the varistor and takes into 
L_SERIES |XXX|          account the elements R_V, R_Z and R_B of the
	 |XXX|          equivalent circuit. The voltage-current dependence 
	 |XXX|          is simulated by a current-controlled voltage source 
	 +-+-+          and is described by the following approximation.
	   |            
	   |            
  +--------+--------+   
  |                 |                                          
  |                 |             log(u) = P1 + P2 + P3 + P4
+-+-+               |                             
\   |               |                 P1 = b1   
|\  |            ---+---                          
| \ | R_VAR               C_PAR       P2 = b2 * log(i)
|  \|            ---+---                    
|   \               |                 P3 = b3 * exp(-log(i))
+-+-+\ U            |                            
  |  |              |                 P4 = b4 * exp(log(i))
  |                 |                              
  +--------+--------+   b1, b2, b3 and be are parameters of the
           |            characteristic defined in file SIOV.LIB.
	   |                    
	   |                    
	   |                      
	   O