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Ron's Web Site
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Date: 7-23-2011
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Number of Hours: 4.00
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Manual Reference:
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Brief Description: Headset Power Supply
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I wanted to use an aircraft DC/DC convertor to provide current for my Lightspeed Headsets, and had put in the related wiring and an adjustable power supply to reduce the voltage to 3 volts, as required by the Lightspeeds. Unfortunately, that didn't work - turning the ANR on resulted in attenuation of not only the noise, but also radio and intercom audio. You could barely hear what was being said at a very, very low volume. One thought was that there was too much noise coming from the power supply, so I added a 1000 µF capacitor, which brought the ripple down from 1% to 0.01%. Cleaning up the ripple didn't make any difference. Thinking about it some more, I remembered there are two kinds of DC/DC convertors: isolated and non-isolated. Non-isolated means the ground is tied to the input ground. Looking around, I found that there are some inexpensive modular isolated 3.3 volt convertors out there for $12-$20, apparently for bluetooth applications. I wasn't able to find 3 - 6 watt convertors that allow trimming the voltage down to 3 volts even, but 3.3 volts isn't that far off from 3.15 volts, which fresh AA batteries usually put out. Anyway, I figured out appropriate connectors, soldered up a prototype board and added a 470 µF capacitor (all that was allowed by the convertors datasheet). That resulted in 0.3% ripple, not quite as good as before, but not noticeable in the headsets. Best of all, the headsets now worked fine. I dipped the proto board in epoxy potting compound in a potting box and installed the convertor in the aircraft
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Top view
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Bottom view
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10 mv Ripple.
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