LTspice
LTspice is a SPICE-based analog electronic circuit simulator computer software, produced by semiconductor manufacturer Analog Devices. It is the most widely distributed and used SPICE software in the industry. Though it is freeware, it is not artificially restricted to limit its abilities. It ships with a library of SPICE models from Analog Devices, Linear Technology, Maxim Integrated, and third-party sources.
Source: Wikipedia
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