ayos, ganda ng discussion dito!
OT: same here sir. nagpalit na rin sila ng mga lines dati pero ganun pa rin disconnected every 5 to 15 minutes from 10PM to 1AM.
depende po talaga sa apps,sir born,sorry nalito ako dito sa discussion,iba naiisip ko regulation vs ripple,ripple po pala yung problem hehehe,btw una kasi basically we have to trouleshoot muna sa regulation kumabaga panghuli na po yung ripple,typical mga ripple consideration nasa 1% ng output(e.g. 5V dapat huwag lalampas sa 50mVpp).yung ripple kasi inherent na talaga yan sa switching elements(meron ata sa power supply magazine ripple theorem by vorperian,i think di ko na matandaan,sa CCM discussion paano nagkakaroon ng ripple)sa mga mosfets at catch diodes,dun naman sa sinabi ko about trr,basically sa budget loss malaki effect nya,sa ripple di naman masyado malaki effect,sa mga switch talaga kumbaga inherent na po yan talaga,pero dun sa nakikita ko sa sukat mo sir kung 5V ang output at 50mVpp marginal po yan dapat po talaga mababa,thanks nga po pala dun sa video ni jim williams sir born,about pala dun sa BW na 100Mhz na gusto mo,masyadong tight po yan,sa mga VRM modules typical apps po yan,kaya po nasabi ko na 20Mhz fairly enough as industry based.sa nakikita kung solution,gagamit ka po talaga ng low esr caps to lower ripple noise.
Thanks for the invaluable info sir icefire. Now we have a yardstick we can use to evaluate the noise performance of our circuit.
Wala bang computation sa mga component values?Actually ito rin ang problema ko sa SMPS;Wala pa akong nakitang procedure papaano ito e desenyo, nakakatakot kasi lalo nat aabot sa >300Vdc ang input nito Sana may mag post ng tamang procedure papaano ito gagawin.Sample problem ko:1. Ano ba ang unang basehan ng component computation, yong Freq ba? o yong Inductor values as per specs ng power supply na gagawin?2. Ano yong detalye ng Output Transformer computation?I been reading SMPS threads hindi ko pa rin makuha
I constructed an adjustable power switching regulator circuit using Allegro’s simple switcher A8447ST, hoping that I could share this circuit with anyone in this forum who would like to explore switching power supplies by building their own. The circuit I came up with is not so different from the datasheet circuit, modifying it just a bit to make it work respectably within desired output voltage range.Using a 24VDC test source and ProDigit 3311 Electronic Load in 1Amp constant current mode as test load, I got a load and line regulation performance figure better than 1%; pretty good for this kind of circuit. Output voltage range measured 0.8VDC to 15VDC, and the IC worked with 80% efficiency at 5VDC output, keeping the IC running cool even at these low output voltage settings. But when output noise was measured, the results were so horrible, better to keep them hidden from view. This is basically a failed project. Why then am I posting it? Believe it or not, It could be more fun when circuits do not work as expected, because failures brings more opportunities to learn new things than some boring outright success. A failure is not a failure at all if you learn something from it. The circuit, being built on a prototyping PCB without the benefit of ground planes and restricting layout, I actually expected it to have a noisy output. It is just that the output noise was far worse than I had hoped for. The problematic noise is the ringing that occurs during the switching transitions that oscillates with about a 100MHz frequency. The main switching inductor is the natural suspect that causes this problem, and it is actually easy to verify this. If I clip the ground wire of my oscilloscope probe on its tip, I actually form a loop antenna capable of picking magnetic fields that happens to pass through the loop. The picture below shows what the probe loop picked up when it was put over the power supply PCB. The toroidal inductor is leaking too much stray fields. Most of this stray energy are coupled with the components around it. There is very little we can do about it; this problem can be solved only by replacing the coil with one that has more adequate shielding. We have to accept the fact the switching noise cannot be fully eliminated with SMPS circuit. The question is more on how much noise can be considered as acceptable? To answer this, I picked one similar simple switcher made by a reputable US company, and measured its output noise under similar test conditions, so that we can have something we can use as a baseline for comparison. This simple switcher is based on LM2576S. The power inductor is the black cube with 101 (100uH) markings. The PCB copper layout can be clearly seen in this photo. During the tests, a 470uF low ESR capacitor was connected through J10 pads, where the regulator output is also drawn out.This is the actual oscilloscope waveforms taken from the J10 output. TDS784D Oscilloscope is band limited to 250MHz, with the vertical channel 1 set to 50mV/div ac coupled. Tek P6139A 1:10 probes are used. Trace shows ripple voltage of about 50mVp-p, with ringing appearing as spikes with 300mVp-p amplitude. Is this noise low enough? I don't know, really . Especially after I watched the video of Jim Williams measuring his SMPS circuit churning out noise at the microvolt level! http://www.linear.com/designtools/video/ltchannel_switchregnoise.jspI seldom build SMPS circuits and lack the experience to say anything with confidence in this field. Master Glutnix is the authority on this subject. I hope mabasa nya ito and throw in his expertise to further educate us.
Adding ferrite beads in series with the inductor? While on my way home- that's one of the few moments when I am not distracted and can do some real thinking, I almost blurted with laughter when I worked the idea in my mind. It was a dumb idea! Really dumb. Buti na lang di napansin ng mga masters ;D.@ Master TipTopThanks again for your important inputs. Like I always been telling everyone who care to listen:PCB LAYOUT IS A PART OF THE CIRCUIT. Identical circuits will perform differently with different layout. Now I can say this is one of the reasons why I post this 'failed circuit'. SMPS circuit is very sensitive to layout, and this case makes a good working example. As for the datasheet recommended layout, this is all taken cared of, at least that's what I believe, taking into account the limitations imposed by the prototyping board. If one is to look at the component arrangements in the picture, he/she can notice the components are arranged in the way recommended by the datasheet. The components are also wired as recommended. Later in fact, I plan to 'violate' these rules to demonstrate to the reader their effects.
Last night, in my home lab, I checked again the noise output of our circuit, and I got results very different from what I got in my office lab. Check this out:This is the noise output I got, without the output ferrite. Way better than the noise level I measured in my office lab (which I am too embarrassed to show) Improvements with the output ferrite installed and a 100uF Tantalum cap soldered across the load side of the ferrite. Note the input is now set at 10mV/div.Same condition as the preceding picture but with oscilloscope bandwidth reduced to 20MHz. Noise out is only 7.2mVp-p!! This morning, I brought the prototype back in my office lab and have it checked again. Noise "the horrible" is back! This means, something is wrong with my instruments! Uh oh... Busy days ahead...
You have a Tek scope at home!!!! Big time!!! Kelan kaya ako magkaroon ng scope?
I cannot be separated with my tek scope very much the same way nucleus cannot be separated with his junebug. So much so, my wife strongly suspect me having an affair with my oscilloscopes.
sir born, are you "doing it" with your scope??? heheheh