Radiation Hardened Latching Current Limiter for Space Applications

The solid-state Current Limiting Switches are widely used in Aerospace applications to improve the operation of DC power systems. These devices, also called Latching Current Limiters - LCLs, are used to protect the DC power bus. They can provide timed action, controlled inrush current and limited overcurrent, avoiding potentially dangerous overloads and surge currents. The switch also creates the possibility to restart the loads that suffered temporary failures. One important issue concerning the use of LCL in harsh environments, especially in space applications, is the radiation effects in its electronic circuit. To avoid these effects, a series of design techniques must be applied to ensure the LCL will work properly. This work presents the implementation and tests of three distinct LCLs, using different controllers. The first controller's circuit uses commercial off-the-shelf components; the second circuit uses a dedicated microelectronics, built in 0.6um SOI - CMOS technology; the third circuit uses a dedicated microelectronics also built in 0.6um SOI - CMOS technology, employing Radiation Hardening By Design (RHBD) methods. All the LCLs use the same model of current sensor and P-channel power MOSFET. The LCLs were submitted to radiation tests using Gamma rays (Cobalt-60) until a total ionizing dose (TID) of 50krad. The test results are presented and discussed. The LCLs supported the applied radiation levels without failure in functional tests. Some parameters had a slightly variation when compared to the original values. Enclosed Layout Transistors (ELT) were exposed to radiation and the VGS(th) were measured.