Smps understanding - Page 1
Forum section: electronics / beginners

author: danman1453
author_rank: Newbie
timestamp: September 18, 2014, 11:58:57 pm
content: I am all googled out. I am looking for a resource to help me understand the design theory behind Smps. I am drawing blanks in regards to the interaction between the inductor and the tank capacitor.IE, if I wanted 3.2 volts at 5 amps, how would I determine the necessary ratings of the components? And where in all this, does the switching frequency come in to play???

author: Kremmen
author_rank: Super Contributor
timestamp: September 19, 2014, 12:29:22 pm
content: Design theory? Then look no further:https://www.coursera.org/course/powerelectronicsIt started beginning of September so you would be late for the early homework but the info of course is there.

author: diyaudio
author_rank: Frequent Contributor
timestamp: September 19, 2014, 06:13:44 pm
content: QuoteSMPS == lots of reading, math, research and experimenting. (There is NO easy way to obtain knowledge in this area)Get hold of some good books and video resources.http://www.diysmps.com/forums/content.phphttps://www.youtube.com/user/rbola35618QuoteIncreasing switching frequency reduces the size of magnetic components. The current trend is to promote SMPS "miniaturisation" by using this method. The maximum switching frequency used to be limited by the performance of available semiconductors. Nowadays however, Power MOSFETs are capable of square-wave switching at 1MHz and beyond. (The physical aspects like layout and parasitics limits switching at high frequencies)

author: danman1453
author_rank: Newbie
timestamp: September 20, 2014, 12:01:39 pm
content: Thanks for the links. I will check them out.As for frequency, is it related to efficiency, or just physical size of components?So if I had no major size constraints, frequency would be a small concern?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 20, 2014, 12:18:37 pm
content: Inductance and capacitance required are inversely proportional to frequency, so you can make the reactive components smaller at higher frequency. But switching losses go up proportionally, and parasitics become problematic (capacitance and inductance that you can't avoid because you necessarily can't construct a circuit of exactly zero size).Tim

author: danman1453
author_rank: Newbie
timestamp: September 20, 2014, 04:33:04 pm
content: Quote from: T3sl4co1l on September 20, 2014, 12:18:37 pmI understand that an ideal circuit would have 100% efficiency. But being what it is, there are losses involved. Am I understanding correctly that as freq goes up efficiency goes down? Due to tighter and tighter component value constraints? Also, with higher frequency smaller components are possible, but are they necessary?I have looked at a few DIY calculators for coming up with the values necessary. A smps running at a set voltage with a max current seems pretty straight forward.I cant find much on a variable supply where the voltage can swing below the supply. Would the boost controller just become a regulator?I am concentrating on just learning the basics for now. I have some specs in mind, being controlled by an MP430 series mcu. It will be battery powered. So efficiency is a mild concern.

author: Yago
author_rank: Frequent Contributor
timestamp: September 20, 2014, 04:39:17 pm
content: Quote from: danman1453 on September 20, 2014, 04:33:04 pmHere are a great series of vids explaining different types of smps and their operation.https://www.youtube.com/playlist?list=PLxaGnte1Dq0lgNtfA9H5Hd_YDyjylThJJBy our very own PostApocolypticInventor, a nice chap

author: danman1453
author_rank: Newbie
timestamp: September 20, 2014, 04:40:33 pm
content: I have watched a couple of his videos. Informative. Still a little over my head right now though.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 20, 2014, 04:42:26 pm
content: Buck: 0 < Vout < VinBoost: Vout > VinBuck-boost: Vout < Vin (i.e., a negative boost referenced to Vin)SEPIC: Vout > 0Cuk: Vout < 0Flyback and forward converters are transformer coupled, so can produce any voltage ratio.I would suggest using some typical controllers like TL494, UC3843, or just building something your self. The purpose of a switcher is generally output voltage, and though it's true you can filter PWM and get a constant voltage, you never want to actually do that directly, because a little overshoot and the current through your switch goes kapow. A switcher is (or should be), first and foremost, a current regulator. You then control the current to regulate the output voltage. You can't use an MCU for this because it's not fast enough.Tim

author: diyaudio
author_rank: Frequent Contributor
timestamp: September 20, 2014, 05:56:02 pm
content: Quote from: danman1453 on September 20, 2014, 12:01:39 pmWith ideal components (zero voltage drop in the ON state and zero switching loss), a converter is 100% efficient. In reality, power dissipation is always associated with every power component.SMPS has n = 80% > There are two types of losses in an SMPS DC conduction losses and AC switching losses.Typical losses are found at the main pass through switcher (normally a IGBT FET), magnetics section transformer and inductor(s), snubber(s), all of these elements work in unison with each other, SMPS efficiency is not related to frequency, frequency is selected based on (as I mentioned before), the physical size of the circuit and is selected based on the magnetics component selected, its also used to reduce switching loses and you may fine tune the a SMPS so the snubber doesn't "clamp" to hard spikes as a result of RLC resonance which is excited based on the selected frequency and pcb layout.The greatest effort is the magnetics theory, its the part most people (even myself) struggle to get right.Forget about using *any* MCU learn SMPS basics, an MCU will just further introduce confusion.

author: danman1453
author_rank: Newbie
timestamp: September 20, 2014, 06:03:38 pm
content: Magnetic as in field strength vs inductance vs energy stored? Thats what I am having a hard time grasping. I cant find anything analogous to it. I think in pictures, so the theories involved are throwing me off.

author: danman1453
author_rank: Newbie
timestamp: September 20, 2014, 06:10:03 pm
content: If running from a battery, is the transformer section needed? I thought the Smps was just the switching part, combined with the energy storage part. As a DC-dc converter isn't the source irrelevant? I am looking at just the switcher, inductor, diode(s), capacitors, and feedback loop.As far as the mcu goes, I am becoming familiar with the MP430 launchpad. I have played with it a bit. Programming is more my style, so I guess I have been looking to incorporate it in because its familiar territory. I know a clock signal is needed to turn the switcher on and off.Do you think a 555 timer clock would be easier to start with?

author: diyaudio
author_rank: Frequent Contributor
timestamp: September 20, 2014, 06:17:45 pm
content: Quote from: danman1453 on September 20, 2014, 06:03:38 pmSorry, I don't have easy answers for you.Read datasheets on high speed transformers, inductors, and SMPS literature there are TONS of things you can study with various degree of depth its up to you to obtain the knowledge. learn by trail and error.I've used products from Arnold magnetics they also acquired micro metals they make some fantastic inductors and SMPS cores I learned lots from their library.http://www.arnoldmagnetics.com/Library.aspx