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Electronics Forum / Basics / December 2006What is this cirquit used for?
Hi group I bougt a toy in the US which is operated by a lippo cell. The wall wart that came along wiht it is obviousely a US version alas working with 110V whereas where I live we have 230V. The wall wart output is rated DC 5.5V 280 mA and is definately only a transformer with a rectifier, a coil and an electrolytic capacitor to flatten out the DC hence unregulated. It plugs into a little box which holds a cirquit acording to the drawing available on the website below. http://mypage.bluewin.ch/mzingg/ From there the wire goes to the toy. I haven't opened the toy since it's difficult to do it without damaging it. I therefore don't know if before the lippo there is more cirquitry or if the box more or less directly connects to the lippo cell. I'm aware that I have to replace the wall wart with a localized version and that I'm fine with one also outputing 5.5V DC @ at least 280mA. I do wonder however what above cirquit does (I figure sereves to cut the wall wart from the lipo once it's full?) and wether it would work to use a 6V wall wart instead cause this is what I would have as a spare one laying around. Getting a wall wart that outputs exactly 5.5V otherwise seems quite difficult. I also wonder wether it would be ok to use a wall wart outputing say 9V and then use a linear regulator and have it output 5.5V DC or if this could negatively affect the loading of the lippo cell. I'm asking cause I don't have much experience with lipo's and know that they can be dangerous if not treated well. TIA Markus > I bougt a toy in the US which is operated by a lippo cell. The wall > wart that came along wiht it is obviousely a US version alas working > with 110V whereas where I live we have 230V. Should work OK if you run it from 100 VAC on 50 Hz. It won't survive 120 VAC at 50 Hz. > Hi group > [quoted text clipped - 32 lines] > > Markus Markus, It's Lipo from Lithium Polymere, a relative new type of battery. The circuit is a simple voltage regulator keeping the output voltage at about the zener voltage. As LIPOs require carefull charging, there should be more electronics inside. You can never count on the stability of unregulated wallwarts. Output voltage is almost 1.5 time the nominal voltage with no- or small load. When you draw the nominal current, they tend to become (too) hot and the voltage drops to - or even below - the nominal voltage. That's why they need the regulator. For the same reason, a 6V wallwart will do fine. A 9V type is not safe as the regulators transistor has to dissipate the excess power and may become too hot. petrus bitbyter [snip] >The circuit is a simple voltage regulator keeping the output voltage at >about the zener voltage. As LIPOs require carefull charging, there should be [quoted text clipped - 9 lines] > >petrus bitbyter Thanks for the help so far. I made a little test and turned my lab power supply to 5.5V and went up to 9V like the 6V rated spare wall wart I have outputs without load. Behind the formentioned regulator cirquit the voltage drop get's a bit smaller (starting at ~5.2V) the higher the input voltage, but it still goes up to 6V (at 9V input). So it apears to me that this simple voltage regulation cirquit is not doing so well. Lacking a 110V AC power source I can't know what the original wall wart really would output, but asuming it would be lower than my 6V supply, I can savely asume that the output voltage would also be lower. I therefore ask if it's not better to completely replace the cirquit with a low drop fixed voltage regulator (LM2940CT in it's standard configuration acording to the datasheet) and feed it from the 6V wall wart I have? I have the regulator and the two capacitors needed here so that would be a quick solultion. Is this a good or bad idea? TIA Markus > [snip] > [quoted text clipped - 38 lines] > > Markus The circuit is not very good and your results seem worse while measuring without load. Guess even a load of - let's say - 1k will show some better results. Nevertheless, a real regulator like the one you mentioned will do better. Think you can even use the existing board and capacitors. When going to 9V input you don't even need a low drop regulator (assuming the smoothing capacitor is big enough). Keep an eye on the heat the regulator has to dissipate. petrus bitbyter > Thanks for the help so far. I made a little test and turned my lab > power supply to 5.5V and went up to 9V like the 6V rated spare wall [quoted text clipped - 13 lines] > wart I have? I have the regulator and the two capacitors needed here > so that would be a quick solultion. Is this a good or bad idea? get a 6V regulated wall-wart off the shelf an stick a 1n4001 in series with the output (get approx 5.4V) or a 7805-based 5V one rated for a little more current than you need and bootstrap it by putting a 1n914 in series with the gournd leg of the 7805. (result about 5.6V) either way should beat the specifications of your original... Bye. Jasen > > Thanks for the help so far. I made a little test and turned my lab > > power supply to 5.5V and went up to 9V like the 6V rated spare wall [quoted text clipped - 25 lines] > Bye. > Jasen The 7805 needs TWO volts more at the input than the output voltage. A small unregulated supply at 9 volts no load will sag below the required voltage, and the output voltage will drop below what you need.  SignatureService to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida >>>Thanks for the help so far. I made a little test and turned my lab >>>power supply to 5.5V and went up to 9V like the 6V rated spare wall [quoted text clipped - 29 lines] > small unregulated supply at 9 volts no load will sag below the required > voltage, and the output voltage will drop below what you need. I once mightily p!ssed off the Principal of a well known Electronics College by proving that his first term class project *could* *NOT* meet the specification of 5V @ 1A using a 'vanilla' 7805 and the supplied 6.3V transformer. He tried to get out of the hole by throwing more reservoir capacitance at it, but I was able to show by a graphical construction that the reservoir capacitance required was ridiculously large. By this time, we had attracted an interested audience of the college lab technician and the instructors for the digital and analog modules (and a decidedly bored audience of the other students in the class). An attempt to demonstrate that the supply did in fact work as designed failed miserably when the current reached about 200 mA with a slight voltage droop which when I insisted a scope was used, proved to be the regulator dropping out and following the bottom of the ripple. I pointed out that if he really wanted to meet the spec, He'd need 78S05 regulators, a mimimum of 8 V rms transformers and heatsinks. Since he'd bulk ordered the parts this did *not* go down well. It turned out that previous classes had 'cooked' their lab reports. As a face-saving compromise, and knowing that we were supposed to be using these PSUs for our digital labwork, I suggested derating the supplies to 500 mA and fitting a much larger reservoir capacitor. Next week, the lab notes had the title "A 5 V, 500 mA Regulated Power Supply" and the larger caps had been purchaced :-) The Lab tech and myself got the assignment of upgrading the class set of these PSUs that got used by the 'foundation' course. We were both amused that a professional engineer could make such a goof on regulator headroom and basic PSU design and I remained close friends with the tech till his death a few years ago. The moral of the story? Even with a humble 78xx series regulator *LOOK* at the data sheet at least once in your career and preferably again before designing it in to anything that isn't a one off project. And *DONT* embarrass the head honcho in public unless you *enjoy* doing scutwork . . . SignatureIan Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED) ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- & [dot]=. *Warning* SPAM TRAP set in header, Use email address in sig. if you must. > >>>Thanks for the help so far. I made a little test and turned my lab > >>>power supply to 5.5V and went up to 9V like the 6V rated spare wall [quoted text clipped - 67 lines] > *DONT* embarrass the head honcho in public unless you *enjoy* doing > scutwork . . . That is because you think too small. ;-) I had a Captain in the US Army who was running around the base telling everyone that it was "Impossible" to convert our B&W TV station to color without replacing everything, including the tower. he was the Base Information Officer, and ranthe base newspaper. he was connstantly sticking his nose into the TV section, and trying to tell the engineers how to do their jobs. After a week of hearing his "No color" crap, I borrowed a color bar generator from another engineer and transmitted our new station ID in color at the start of our live 6:00 PM newscast to be sure that a lot of people would see it. He was really pissed off. He was screaming that I had made a fool out of him, in front of the whole base. I smiled and said, Sir, You always bragged about being a self made man, then reminded him that he was tresspassing, and I could have him arrested for interfering with my duty. As he left he infomed me that he was calling the USARAL General. I don't know what the General told him, but I never saw him in the Transmitter / Control room again.* He would just go to his end of the building to cut & paste the layout for our base newspaper every week. SignatureService to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida >> or a 7805-based 5V one rated for a little more current than you need >> and bootstrap it by putting a 1n914 in series with the gournd leg of >> the 7805. (result about 5.6V) >> >> either way should beat the specifications of your original... > The 7805 needs TWO volts more at the input than the output voltage. A > small unregulated supply at 9 volts no load will sag below the required > voltage, and the output voltage will drop below what you need. That's why I mentioned excess current cabality, less sag. in any case, given the regulation of his original a little sag is unlikely to be a problem. Bye. Jasen > >> or a 7805-based 5V one rated for a little more current than you need > >> and bootstrap it by putting a 1n914 in series with the gournd leg of [quoted text clipped - 9 lines] > in any case, given the regulation of his original a little sag is > unlikely to be a problem. A couple volts is "A little sag"? SignatureService to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida > Hi group > [quoted text clipped - 10 lines] > > http://mypage.bluewin.ch/mzingg/ It's a 5-V regulator. > Hi group > [quoted text clipped - 32 lines] > > Markus what ever you do, get the proper charger with the correct input voltage. and make sure it does not deliver any more current than what you are using now.. Lithium cells can go up in a violent fire... be careful with current to a LI cell. Signature"I'm never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5 How many wires on the primary of the wall wart? Maybe you can restrap it for 240 |
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