
Switched and Averaged Pspice Models
Page 4 / 20 AN-PSM-11
V1.0
1 Preliminary remarks
The simulations described in this document were carried out with PSpice V8.0
Version V2.0.
1.1 Description of the converter symbols
All the symbols used in the converter circuits have the same structure.
Inputs
ue: Connection for the input voltage.
d1: Input of the averaged pulse control factor d
1 for controlling the converter.
CAUTION: This input is not restricted to values between 0 and 1. Meaningless
pulse control factors (e.g. d1 = −0.5) can therefore be specified. (Limiting occurs
in the pulse-width modulator).
Outputs
ua: Connection(s) for the output voltage(s).
Ud: Drain connection of the external switching transistor.
d3: Output for display of the operating mode and length of the interval d3Ts (inductor
current iL = 0). d3 = 0 means the converter is operating continuously. For
example, d3 = 0.3 means the converter is operating discontinuously and the
time duration of the interval is d3Ts =0.3 * Ts (Ts is the switching period).
dis: Output which describes the slope of the switch current in the interval d1Ts. This
quantity is necessary for current loop operation. In the case of a “single-
inductor-converter”, dis is equal to the slope of the inductor current iL in the
interval d1Ts. In the case of a converter with several inductors, however, it is a
weighted linear combination of the inductor currents.
iL: Output for the averaged inductor current. In the case of a converter with one
inductor it is the mean value of the current through this inductor. This quantity is
important for current loop operation.
eta: Output which indicates the efficiency of the circuit. CAUTION: The output
supplies meaningful values only in the steady-state condition and with DC
analysis. Moreover, it serves only as a point of reference, as, of course, the
switching losses of the real converter are not taken into account.
With all models, variable parameters are represented in the symbol and can be
edited by double-clicking. The variable values can be either figures (e.g. L = 50uH) or
parameter values (e.g. L ={L1}). For latter, the parameter values must be defined in
the circuit by a PARAM block.
Every averaged model has a null parameter. This parameter serves as a
convergence aid. PSPICE experiences difficulties if an expression in an EVALUE
source in IF commands is to become zero. Example:
E3 IF (V(dss)-Dmin>0, V(dss),Dmin)