I'm hoping this is the kind of thing we can just buy rather than build, but open to building. We need to take a 12V DC in from a marine battery and power a Raspberry Pi (5v), camera (9v) and AES receiver (12v). Can anyone tell me what the smart way to do this would be? I don't know enough to know if I should be looking at buck converters or linear regulators, pointers welcome.
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2\$\begingroup\$ Look up DC-to-DC converters. You can definitely buy them, but where or what to buy is off-topic here on EE.SE. \$\endgroup\$– user2943160Commented Aug 28, 2016 at 17:00
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\$\begingroup\$ Car usb charger for the 5V. Then another and change the resistors inside for 9V, or any car 12V to 9V charger... \$\endgroup\$– PasserbyCommented Aug 28, 2016 at 17:14
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2 Answers
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You didn't give us the all-important information of how much current you need at each voltage.
For the 5 V a buck converter is most likely the best answer. A linear regulator would dissipate 7 V times the current. That's only 140 mA output to cause a watt of dissipation.
For the 9 V output you have less of a voltage drop, so a linear regulator might be OK. It takes 330 mA output to cause a watt of dissipation. If you need 150 mA or less, then a 7809 in free air would do, and would be 75% efficient. However, unless you know the 9 V current is low, I'd go with a switcher here too.
At this voltage, there are many off the shelf switcher chips out there. You supply a few external components, like inductor and input and output caps, hook them up like the datasheets says, and they work. If you think this is beyond you or don't want to bother, just buy two off the shelf DC to DC converters. They will cost significantly more than buck chips with the parts around them, but are really easy to use and just work. For a one-off, the few extra $ may be irrelevant.
answered Sep 28, 2016 at 17:36
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You can use DC to DC converters like answered before. I would convert the 12V to 9V with a first converter, and from this 9V I would create a 5V with a second converter.
Linear converters should be ok if you don't draw too much current (usually less than 1A). If you need more, the converters could overheat. In this case you could look at switching converters, which are much more efficient, hence less overheating.
