Need help with my first "real" project, a 12, 10, 8, 5v switch mode power supply - Page 1
Forum section: electronics / beginners

author: atsch
author_rank: Newbie
timestamp: October 02, 2014, 09:06:59 pm
content: I've been working on a robotics project for a while, and I've come across some power problems. I need a *ton* of different voltages, and my original linear regulator design is really inefficient.Here's what I need:12 at 6-8 Amps (4 12v motors taking 2 Amps at max speed each)10v for an (up to) 10 Watt LED (don't ask)8v for motor controller and arduino (arduino has a built-in regulator)5v to decrease load on the arduino's built-in regulator for high-power Ultrasonic and infrared sensorsHere's how I've been doing it:3 * 7812 (2 amps) in parallel (big regulators are terribly expensive)resistor takes power from 12v regulators for LED (it dims when the motors start moving because the motors spike in power draw)3 amp 7808 for motor controller and arduinoarduino internal 5v regulatorBTW, this whole thing is powered by two 20c 7.4v Li-Po batteries in serial, nearing 12v when emptyas you can see, this is supremely suboptimal, and I need a replacement, however my electronics experience is practically nonexistent, I've only used development boards and made some simple sensors (e.g. high power reflected light sensor), so I need your help.My fist thought was building a switch mode power supply for my 12v needs, and powering the rest via linear regulator. However there is a bunch of problems: I can't put anything behind the 12v regulators because the initial power draw from the motors is insane (Would a beefy capacitor help?), and I'm sure 78XXs don't appreciate PWM flicker that much.So instead of putting the 8v stuff behind the 12v regulators, I have to put them in parallel, which brings me back to my problem of wasting a bunch of energy (12W according to my calculations).What is an good solution to this problem? Every solution I come up with just ends up being a bad Idea in some way, and I'm sure there's a common way to deal with this.

author: tggzzz
author_rank: Super Contributor
timestamp: October 02, 2014, 09:31:36 pm
content: Why do you have to use linear regulators?There are many ready-made switched-mode DC-DC converters which won't "waste" power.

author: atsch
author_rank: Newbie
timestamp: October 02, 2014, 09:36:53 pm
content: I have yet to find a ready-made switch mode power supply that can can supply 12v at 6-8 amps. I could of course use premade PSUs for the other voltages, but with space at a premium I feel like it is much more sensible to make my own power supply.

author: Riotpack
author_rank: Regular Contributor
timestamp: October 02, 2014, 10:45:47 pm
content: What about something like thishttp://www.airyear.com/ltc3780-automatic-buckboost-module-red-8a-p-110345.html?zenid=41cf1acafcb591bc79d1988ff1493f26I would soft start motors running from a SMPS, especially if more than one is starting at the same time.It's a buck-boost, so it doesn't need the ~2v overhead of a standard linear reg.

author: Riotpack
author_rank: Regular Contributor
timestamp: October 02, 2014, 11:06:53 pm
content: If you want to design your own take a look here -http://www.ti.com/ww/en/simple_switcher/design-tools.htmlYou may have to go for a buck/boost design due to your Vin equalling or very close to your Vout when the battery is at its low point.