Published:2011/8/4 1:16:00 Author:Amy From:SeekIC
Ton Giesberts
Main power supply
The compactness of the amplifier is offset by the sheer mass of the power supply. Of course, we could have also developed a switch-mode power supply, but it would have to be a supply that could deliver a good 40 A at a bit less than +/- 60 V. That would be a challenge, to put it mildly. It should thus be clear why we choose to use a conventional design.
In consideration of the current levels involved here, we selected a heavy-duty rectifier that can handle a rated current of 46 A and a peak current of 90 A. For the electrolytic capacitors in the power supply, we selected types that can handle strong ripple currents. Normal power-supply electrolytics are not intended to be used in such severe applications. From the BCcomponents 2222 154 line, we selected a capacitor that can handle ripple currents of around 11 A at 10 kHz (or 20 A at 100 Hz) and has low values of self-inductance and ESR (a tall electrolytic capacitor with a small diameter). A long service live is ensured by connecting four capacitors in parallel for each half of the power supply. Here we can give you a small tip: if you order ten capacitors in a single lot from Famell, it will cost you less than buying eight of them at the single-quantity price.
If you think the power supply is perhaps somewhat over-designed with the specified component values, we wouldn’t immediately disagree. However, you should bear in mind that at 2 x 200 W sine-wave power, the output voltage of this supply already drops by 5 V!
Protection
The mains voltage is routed to the power supply board via K4. The primary fuse for the main transformer (F4) is also fitted here, so it isn’t necessary to use a mains connector with a built-in fuse. The mains voltage for the auxiliary voltages is tapped off after the fuse for the main transformer. If the primary fuse blows, power will also be removed from the rest of the amplifier. In the opposite case, a similar situation exists. If the fuse for TR1 and TR2 blows, the supply voltage for the mains switch-on delay circuit will drop out, and power will be removed from the entire amplifier. A situation in which only part of the amplifier is without power can occur of Fl and/or F2 blows. In this case, at most the +5 V supply voltage will be lost, and there will no longer be any signal. That will not have any further detrimental effects; the most that can happen is that a small ’pop’ will be heard from the speakers.
For additional safety, the main supply voltage for the final amp is protected using two 16-A FF fuses in 32-mm cases. This ensures that the voltage decays as quickly as possible in case of a short circuit, rather than requiring the power supply capacitors to first be discharged. These fuses are also fitted on the power supply board, and they are connected between the large power supply capacitors and the amplifier board using screw-mounted flat connectors (car connectors). The advantage of using separate fuse holders is that the PCB-mount fuse clips used here can handle a continuous current of no less than 15 A (with adequate copper area on the circuit board). Most PCB fuse holders are only rated at 5 A continuous current.
Reprinted Url Of This Article: http://www.seekic.com/blog/project_solutions/2011/08/04/ClariTy_2x300W_Class_T_Amplifier_Part_3__power_supply_assembly_and_alignment_(3).html
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