Circuits for protecting and triggering SCRs in high power converters

The performance of high-power converters employing silicon controlled rectifiers (SCRs) operating at several kilovolts and switching several thousands of amperes is strongly dependent on the triggering circuit and the protecting circuit (snubber) used. In this paper two standalone trigger circuit topologies are discussed and test results are given for one of them in particular, built with off-the-shelf components. A standard snubber circuit configuration was used and its ability to protect the SCR was examined by classical analytical methods and by computer simulation. Results of these calculations are reported as well as predictions about the fault tolerance afforded by the snubber design to a high power converter using SCRs. Since the components of the SCR protective circuits strongly affect the overall package size of the converter and tend to determine the minimum size and weight achievable, a conceptual design is also presented for a combined snubber-trigger circuit with the potential for reduced size and weight for the whole assembly.