A Hard Off-the-Shelf SG1524 Pulse Width Modulator

Samples from three lots of SG 1524 pulse width modulators and from four manufacturers of LM139 quad comparators were irradiated in cobalt-60 to determine total dose effects. Within the context of our INTELSAT V circuit designs, the SG1524 demonstrated a damage threshold of about 0.8 Mrad, which was an order of magnitude more radiation hardness than the best LM139. The source of this hardness may be partially due to lower betas and some manufacturing processes which have previously been shown to be effective in hardening LM108's. The variation in LM139 hardness needs further investigation. The SG1524 contains an oscillator, regulator, comparator, error amplifier, on-off control, and other important functions necessary to spacecraft power conversion equipment. A dc/dc converter designed around the SG1524 has the same power consumption as one designed around the LM139; but, because fewer parts are required, the overall weight is less and the circuit reliability is higher. Changes in the electrical parameters of both parts were examined as a function of the logarithm of the total radiation dose between exposures ranging from 0.02 to 1.0 Mrad. Degradation comparisons were based on the upper 95 percent confidence limit around a least-squares fit to a second-degree polynomial.