Argh - I now recognize the circuit. Simple circuit - I was just getting thrown off by all the caps and rectification stuff. Anyways - that sort of design is way to inefficient for my use - I really need this supply to be as efficient as possible. Anyways - Does anybody have an opinion on how those transformers look? Or does anybody have a suggestion for a better transformer? (preferrably lower voltage) Thanks!
Maybe this will work for you? According to the data it will supply about 2.5A max at 12v resulting in a 30W small powersupply. You can choose to either modify the output voltage with an external switching regulator or modify the original circuit for 5v operation. Effeciency, according to the sheet is >80% and you get to wind your own transformer.
The drawing was fixed. It was wrong, but now it's right. However, 125k used to represent 0.125uF is not a good practice. It would imply "125kpF", and that's like using "mkg" to mean a gram. Yes, I've seen power supply designs like that. Of course, they deal directly with mains voltage, not exactly what a beginner should be dealing with. The main cap should be rated for constant connection to the mains (such as the X2 rated ones typically used for noise filtering). In addition to a fuse, there should be a fusable resistor with a value of roughly 100R to limit inrush current and stop the current in case the circuit is connected to a cheap inverter or UPS. Otherwise, the increase in current due to harmonics may destroy components or even start a fire. Therefore, I don't recommend those circuits for products that are to be sold, and if you do anyways, include a disclaimer that the product should not be used with dimmers or cheap inverters/UPSes. Otherwise, lawyers may be going after you soon.
Here's an example of a simple circuit using a transformerless 5V supply, from 240V mains As you can see, it doesn't need to be really elaborate if it's designed well.
Are you suggesting I built that entire circuit? That circuit is about 3 times the size of the entire rest of the board... I'd feel a bit silly...
I ment to board mount the small board inside the cellphone adapter, it only has 4 or 5 connections, so there are no problems doing that.
I don't see how you can get any smaller and effecient than utilizing a switching powersupply, unless your power requirements are very small and you trust the product you are building not to have a meltdown if anything goes slightly wrong.
Hmmm - then I must be looking at it wrong. Could you please explain the circuit? I'm not even sure which pins on a PIC are for power... (being an AVR man myself)
There is no PIC controlling the circuitry if that is what you are asking. It, the TOP245Y, basically chops up the rectified line voltage to a higher frequency so that the step-down transformer with the help of U3 (adj. zener shunt regulator) will attain the correct voltage at a much higher effeciency. Therefore less energy is wasted and you will not need any of those bulky transformers for higher currents. Although I would personally suggest that you just buy an adapter that plugs into the wall since the cost of these components could easily outstrip the cost one 5v general purpose adapter. Even one that is of higher voltage would do, just add two capacitors, a diode, and a 5v regulator with maybe a heatsink and you would have your powersupply.
It's very common to see suppression/mylar/polypropylene capacitors maked with 125k to represent a 0.125uF. Blame the capacitor manufacturers not us!
Are you sure this isn't the IEC cap convention with 12 x multiplier of 10^5, in pF, and K for 10% tolerance? That would give 1.2uF, a stock E12 value, and (just) enough currrent to drive a small relay on the end of the logic.
I remember reading somewhere in my notes that certain capacitor manufacturers elect to use odd units rather than uF, pF etc. It's possible that this capacitor could have a 10% tolerance however.
Well I found a company that makes *exactly* what I'm looking for: http://www.biaspower.com/ I've been in contact with a salesperson there and the only problem is that they're very new and the parts haven't made it to production yet, and won't for a couple months, so they don't even have samples yet. Argh. Anybody know of any companies that make a similar product? Again - this is EXACTLY what I'm looking for.
I found a circuit that uses a very small pulse transformer and gives isolation! http://www.discovercircuits.com/PDF-FILES/acdc1.pdf Just something to use the next time someone needs something like that.
If direct connection to 110 or 230V mains (no isolated output) doesn't bother you, you can use Maxim's MAX610 for +5VDC output up to 50mA (or possibly a MAX611-612?). CD
Interesting chip - is it still in production? I can't find it on Maxim's site - but I was able to find a datasheet elsewhere: http://www.selectronic.fr/includes_selectronic/pdf/Maxim/MAX_611.pdf It would also work - though for this project bias power is sending me some parts to test out, so I'll probabaly end up using those. They're somewhat big though - so in the future I think these maxim chips would be better - but none of the distributors I use carry them.
I can't find it neither on Maxim's site , but my local store has it still in stock. Price is 7.70 Euro (about $9.30). CD
Hrmmm - that datasheet is dated 1994... I guess maybe they're out of production now or something - but you'd think they'd still be mentioned on their website... Anyways a couple modules from Bias Power arrived today. They look like they're going to work out perfectly. Now if only they'd get them into full production... Lazy punks...
why cant you just get a tiny board mount transformer, 4 diodes, 4 caps and a 7805 regulator? cheap and easy, and isolated. need a schematic?
