larsie 121 Posted February 22, 2012 Share Posted February 22, 2012 Does anybody know of a really cheap circuit/component that I can use to power an MSP430 from 230V? Basically a cheap way of getting 3V DC (low current) from 230V AC... Quote Link to post Share on other sites
chibiace 46 Posted February 23, 2012 Share Posted February 23, 2012 one of those wall wart power supplies to get you down to something workable like 5v-30v. if your using the launchpad you can use most of those usb chargers directly into the programmer. Quote Link to post Share on other sites
JWoodrell 285 Posted February 23, 2012 Share Posted February 23, 2012 Most people have junk cell phone chargers lying around, if they are 110V you can take and wire the transformers in series, then take the 5v output and zener it down pretty easy. and with little power as it needs ANYthing will work pretty much larsie 1 Quote Link to post Share on other sites
nuetron 64 Posted February 23, 2012 Share Posted February 23, 2012 Have a look at this: http://www.falstad.com/circuit/#%24+1+4 ... -4+2+-1%0A Just an idea I've been toying with. Don't trust the simulator completely, I've fooled it on many occasions! larsie 1 Quote Link to post Share on other sites
amykyta3 4 Posted February 24, 2012 Share Posted February 24, 2012 @nuetron: Close, but that design will vary depending on the load. I would've linked you directly but this is a new account so I can't post URLs. Do a google search for "Make a Transformerless Power Supply - Bright Hub". It should be the top result. The last one on that page is the best since it electrically isolates the circuit from the mains. This one produces 12v that is somewhat regulated by the zener diode. I would then put a typical 3.3v linear regulator at the end to power the msp430. larsie 1 Quote Link to post Share on other sites
RobG 1,892 Posted February 24, 2012 Share Posted February 24, 2012 Why don't you just buy a small, cheap switcher? Also, checkout this thread. larsie and nuetron 2 Quote Link to post Share on other sites
larsie 121 Posted February 24, 2012 Author Share Posted February 24, 2012 Regarding the brighthub link (thanks), another forum was very critical and said it wasn't isolated. I guess a cap can isolate dc, but ac?? Don't think so. I never really listened when my lecturers talked about ac... http://www.electro-tech-online.com/elec ... esign.html And thanks, RobG for that post. Can't believe I missed it in my search. Quote Link to post Share on other sites
RobG 1,892 Posted February 24, 2012 Share Posted February 24, 2012 Forgot to add, I am using that switcher in my project. Quote Link to post Share on other sites
amykyta3 4 Posted February 25, 2012 Share Posted February 25, 2012 another forum was very critical and said it wasn't isolated Its isolated enough to be safe. With both hot and neutral wires having a cap on them, it allows the circuit's DC component to float to match the chassis/person handling it. As long as the capacitors are small, they will not be able to transmit enough AC current through them to be able to do any damage. In fact, I'm quite sure the little USB wall-plug adapters for your cell phone use capacitive coupling the same way. The forum you linked did bring up a few good points, although a little bit of an overreaction. Probably want some higher-rated capacitors on the mains end. Also, the linked PDF does a nice job explaining the concepts. Either way, If you end up doing a transformerless design I'd still recommend using caps on both Hot and Neutral lines. Never assume that neutral is actually neutral. Always assume that a bad electrician/cocky homeowner will muck this up and then you'll have "ground" be at 230 VAC in relation with the real ground. RobG and larsie 2 Quote Link to post Share on other sites
nuetron 64 Posted February 25, 2012 Share Posted February 25, 2012 Another circuit idea: http://www.falstad.com/circuit/#%24+1+4 ... 05+1+-1%0A This one uses a 3v zener, and uses the output as a reference. Quote Link to post Share on other sites
jim940 28 Posted February 25, 2012 Share Posted February 25, 2012 Many cell phone USB chargers and laptop chargers today can switch from 120V/230V without a issue. Cause its cheaper to make one set of internals for everything then not nowadays. Check the back of your chargers, you might have one waiting and available already. World wide all companies do is change the plastic plate that faces the wall with the appropriate plug configuration during manufacture in their last operation so it costs no where near as much as running dedicated lines producing different adapters for different markets. Or in the case of laptop AC Adapters is provide you with a different 3ft length of cable with the appropriate plug attached to that instead of the expensive part (the AC/DC adapter itself). My Nokia cell phone charger is rated for a input of 100V-240V @ 50-60Hz and outputs 5V DC at 1.2A. As the examples closest to my desk that will give you your 5V DC and if your really cheap to drop the $5 5V power from the adapter do what oPossum does, use a LED to drop it down to ~3V. Jim nuetron and larsie 2 Quote Link to post Share on other sites
larsie 121 Posted February 25, 2012 Author Share Posted February 25, 2012 another forum was very critical and said it wasn't isolated Its isolated enough to be safe. With both hot and neutral wires having a cap on them, it allows the circuit's DC component to float to match the chassis/person handling it. As long as the capacitors are small, they will not be able to transmit enough AC current through them to be able to do any damage. In fact, I'm quite sure the little USB wall-plug adapters for your cell phone use capacitive coupling the same way. The forum you linked did bring up a few good points, although a little bit of an overreaction. Probably want some higher-rated capacitors on the mains end. Also, the linked PDF does a nice job explaining the concepts. Either way, If you end up doing a transformerless design I'd still recommend using caps on both Hot and Neutral lines. Never assume that neutral is actually neutral. Always assume that a bad electrician/cocky homeowner will muck this up and then you'll have "ground" be at 230 VAC in relation with the real ground. Thanks. I'll test the circuit. In Norway, where I live, many installations have both wires as live. Something like 135 V compared to ground, but 235v between the two live wires. Quote Link to post Share on other sites
oPossum 1,083 Posted February 25, 2012 Share Posted February 25, 2012 Regarding the brighthub link (thanks), another forum was very critical and said it wasn't isolated. I guess a cap can isolate dc, but ac?? Don't think so. I never really listened when my lecturers talked about ac... http://www.electro-tech-online.com/elec ... esign.html This type of capacitive reactance supply can be safe and effective if properly designed and implemented. That link, however, is a very flawed and unsafe design. There are critical components missing and improper component selection. The explanation of how it works is inadequate and significantly incorrect. Using this type of power supply seems like a bad idea if you are unable to recognize the errors in designs posted on the internet. Quote Link to post Share on other sites
dkedr 31 Posted February 25, 2012 Share Posted February 25, 2012 Another circuit idea: http://www.falstad.com/circuit/#%24+1+4 ... 05+1+-1%0A This one uses a 3v zener, and uses the output as a reference. Have a look at this: http://www.falstad.com/circuit/#%24+1+4 ... -4+2+-1%0AJust an idea I've been toying with. Don't trust the simulator completely, I've fooled it on many occasions! I've noticed that you're using 230V on the AC supply on the simulator. You have to use 330V there as the simulator uses that as the peak voltage, and the 230V AC rating on mains is RMS. Using the correct mains supply makes your first circuit output over 4V, and the second one get's a big current spike. Quote Link to post Share on other sites
nuetron 64 Posted February 26, 2012 Share Posted February 26, 2012 I've noticed that you're using 230V on the AC supply on the simulator. You have to use 330V there as the simulator uses that as the peak voltage, and the 230V AC rating on mains is RMS. Using the correct mains supply makes your first circuit output over 4V, and the second one get's a big current spike. In the second design a TL431 variable shunt regulator can make the Vout adjustable, and change the caps to 1000uf to make the current spike negligible. Quote Link to post Share on other sites
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