Temperature tracking SPICE macro-model for laser and LED driven opto-coupler assemblies

Temperature tracking models for opto-coupler assemblies constructed from discrete components were developed. These opto-couplers used a photon source consisting of either a laser diode or a light emitting diode (LED) coupled to an AlGaAs photodiode through a lens. These assemblies are different from most of their integrated circuit counterparts because a photodiode is used for a detector rather than a phototransistor. Although, in the intended use, these assemblies couple digital-like pulse trains, they are analog devices capable of operating over wider ranges of voltage than most digital devices. Robust models which accurately simulate over these voltage ranges were desired. The model was needed to help assess the design margins of a large and complex circuit in which the couplers are used. This process requires a large number of long simulation runs, so simplicity was given a high priority. The simple SPICE model for an opto-coupler assembly constructed can be used to accurately simulate the operation of assemblies made up of different types of discrete devices over a temperature range of -55 to 75°C using a single set of parameters and a TEMP statement available within SPICE. Measurements taken from one of each type of device were used for the extraction of the nominal values for the model parameters. The simulation results agree well with the measured data for both assemblies