ClariTy 2x300W Class-T Amplifier Part 3: power supply assembly and alignment （5）

Published:2011/8/4 2:13:00 Author:Amy From:SeekIC

Ton Giesberts

Alignment

The only alignment that is required is to adjust the dc offsets of the outputs, which can be done after the amplifier is assembled but should preferably be done during testing before final assem­bly. Naturally, the dc offset voltages must be set to zero. The offsets must be adjusted (using PI and P2 on the amplifier board) with the amplifier switched on and operating in normal mode (not muted), with its rated load but without any drive signal.

In the mute mode without any load, the amplifier has an output impedance of approximately 10 kft. In this situa­tion, there will be a small voltage on the output, but this does not have to be adjusted.

Besides adjusting the offset, the only other alignment is the dead-time set­ting for the MOSFET drive circuitry. This is determined by the positions of jumpers JP1 and JP2 (or BBMO and BBM1). Set the dead time to 80 ns by setting JP1 to T and JP2 to ’0’. There’s no point in experimenting with other values. Using a larger value causes increased distortion, and using a smaller value causes short-circuit cur­rents to flow through the MOSFETs, which can be fatal for them.

All possible settings are listed in Table 1. The component overlay on the amplifier board also clearly indicates the proper positions of the jumpers.



Final remarks

There are a couple of things we still have to tell you. The first is that the amplifier can be used bridge configu­ration, as explained in the ’Two chan­nels in bridge mode’ text box. Another essential aspect is the measured per­formance, which is also described in a separate box. The measurements were made using the complete amplifier, which means including the niters. Unfortunately, there is not enough room to describe the filter circuits in this article. For the time being, you can also use the amplifier without the fil­ters, but we strongly recommend including them in the overall system.

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