Simulating the MC34063 in Inverter Configuration with an Accurate TL431A Model

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Please download the file: The files include an example of the MC33063's inverting configuration with the IC's ground pin floating at the negative output voltage. Be sure to unzip all files into the same folder so that LTspice can find the hierarchical files.

Note too that the files include a very accurate LTspice specific model for the TL431A as well (this IC is especially well suited to combine with the MC33063 type switching regulator). Normally the output of the MC33063 regulates output voltage by operating in bang-bang mode between zero current and its current limit. This mode of operation is noisy, chaotic and produces excessive ripple voltage. By combining these two low cost ICs standard continuous current mode operation can be achieved.

For those interested in creating their own high performance (i.e., both fast and accurate) LTspice specific behavioral models, please carefully examine these two examples in detail. The MC33063 model in particular combines a ground referenced behavioral interior logic core (which is much better for simulation performance) with fully floating devices connected to the IC's external pins.

Also be sure to note extensive use of the performance enhancing built-in "parasitic" elements that are available in LTspice. Use of these enhancements both cuts down on node count and improves convergence performance.

Another technique to note is the use of LTspice's level 2 behavioral diode and switch models. These yield continuous I-V characteristics with continuous derivatives, which greatly enhances convergence performance (see Help for usage details). -- a.s.