118-watt LT1166 auto bias the QFET MOSFETs output stage with LTC6090 input stage.

Project 75 features the LTC6090 at the input stage and the LT1166 automatically adjusts the bias of the power QFET MOSFET output stage devices. The prototype achieved a measured power output of 118.97 watts into an 8Ω load with a ±45VDC power supply.

This project demonstrates the ability of the LT1166 to match with any power MOSFET devices in the output stage and to properly set its bias current. This feature avoids thermal runaway at its operating point.

The prototype utilizes an odd combination of FQA28N15 and FQA36P15 in the output stage, but the LTC1166 has no problem adjusting the correct bias as shown in the project's test results.

The QA400 audio analyzer measured the THD+N at 0.00226% and a flat 20Hz to 20KHz frequency response.

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