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Switch-mode power supplies — Parallax Forums

Switch-mode power supplies

Peter JakackiPeter Jakacki Posts: 10,193
edited 2011-08-13 16:25 in Propeller 1
Although this is not Propeller specific nonetheless the post is directed to fellow Prop'ers where frequently discussions about power supplies pops up. A lot of members just use linear regulators because they are nice and easy whereas switchers sound too complicated. Then when someone does use a switcher they end up with a big TO220 pack device and big caps etc (ugly).

The point of this post is to highlight how simple a switcher can be and just how compact too. Have a look at this small module (it's one of mine), it measures just 0.78" x 0.45" with an overall depth of 0.3" because of the inductor on the reverse side.
SM5010A module-m.jpg

The 7 pins are 0.1" spaced and allow for on/off control and adjustment of the regulation voltage which is normally set to 5V. There's also a 3.3V LDO regulator onboard that doesn't break a sweat or even get warm even at 250ma load. As you can see there are no big electrolytic or tantalum capacitors in sight, just cheap ceramics. It's based around a LM5010A which can operate at up to 1MHz switching frequency and up to 75V voltage input. The standard components that I use on this will allow it to operate up to 50V as is. Total cost of parts per module is less than $4 but it means a small footprint, high input voltages and output currents up to 1A.

OK, that's my design tip for the day.
SM5010A module-m.jpg
800 x 445 - 96K

Comments

  • Cluso99Cluso99 Posts: 18,069
    edited 2011-08-11 01:09
    Nice job Peter!
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2011-08-11 02:19
    Cluso99 wrote: »
    Nice job Peter!
    Thanks mate, just a few notes here for forum members.

    In comparison to a linear regulator it covers the same area as a 7805T (without heatsink) in a TO220 pack when you lay them both flat. For a test I hooked up a 7805T without a heatsink to the same 500ma test load and by the time I had cranked the input supply up to 9V the regulator was running that hot I couldn't touch it. To dissipate that kind of heat needs a good heatsink and good ventilation assuming that the ambient temperature is being kind which is not always the case. I would not try running the 7805 at voltages much higher than 12V then and definitely not at 24V (even much less 48V). At 24V the 7805 would be "trying" to dissipate 9.5W and that kind of heat would burn the PCB it's on unless you had a huge slab of metal to spread it. The thermal resistance to air of a 7805T is 65'C/W!!!

    The little 5010 switcher doesn't even feel like it's turned on as it's running just as cool as if it's off.

    So a linear regulator might be rated for 1A but doesn't mean you can get it easily if at all.
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2011-08-11 02:28
    As I have a load of Li battery cells, from laptop batteries, cameras and phones, what I always crave for is regulator that could regulate or boost/buck the 4.2 V - 3.7 V to 3.3 Volts. The LDO ones that I have looked at always seem to have a huge quiesant current spike at the low end.

    Perhaps the way out of this would for me to boost 3.X V up to 5.0 V and then drop it back down again (5 V is always useful). This route would still be smaller and certainly more efficient than two Li cells and my usual twin regulation down.
  • idbruceidbruce Posts: 6,197
    edited 2011-08-11 02:40
    Peter

    Very nice project! What are you going to do with this?

    Bruce
  • pacmanpacman Posts: 327
    edited 2011-08-11 03:12
    So how can I buy some?
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2011-08-11 03:56
    Hi Bruce and pacman,

    This is just a general-purpose switcher module that I use in a lot of my designs. It is footprint compatible with and replaces an earlier generation of switchers that ran at lower switching frequency with larger caps etc. I will probably look at getting these made up externally in some volume if the price is right etc. At the moment they are for internal use but if I do get them manufactured in volume then I could make them available. Even so I could probably make a small quantity available for now at a reasonable price (but not $4).

    BTW, I could design a switcher straight onto the target PCB but this module fits into tight spaces and also makes it easier on the PCB layout etc.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-08-11 05:13
    Nice work. Is the secret in the very high frequency? Which then makes both the inductor and the capacitors smaller.

    I've been using switchers for several years now and your design is a quantum leap in terms of size. Do you have a parts list?
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2011-08-11 05:36
    No secret really although it is a case of doing your research. So many designs are based on the older generation "Simple Switcher" which is really decades out of date. Of course these devices are easy to attack with an arc welder but that's about it. I scrounged through device after device (and price after price) until I found this gem. My earlier design just used a small 8-pin SOIC chip which was just as small a module but needed larger caps and tantalums at that plus it only went up to 37V and 500ma.

    You can check out a design on national semi's website www.national.com and create a login then go to webench where you can test your design and it does all the sims and boms etc. A very powerful tool but you have to do your own pcb, it won't do that for you :)

    I used it's values as a basis for my design but I didn't follow it verbatim. The design worked first time, even when I (after donning safety goggles) cranked up the input voltage and loaded it right up, no magic smoke!
  • prof_brainoprof_braino Posts: 4,313
    edited 2011-08-11 07:53
    Very cool. If I read this right, this is the new way to go. Its more efficient, more flexible, has a similar footprint and price. Sounds too good to be true. What are the drawbacks, aside form being new? Is there anything to watch out for, like interference from the switching frequency?
  • LeonLeon Posts: 7,620
    edited 2011-08-11 07:57
    Meeting FCC and CE EMC requirements can be difficult.
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2011-08-11 08:04
    I run at a more leisurely pace of around 600KHz and since the design is very tight and off the main board I don't have a lot of problems with EMC (normally). The types of input caps that are on the module are important as a lot of switching noise can be transmitted back over this. Of course these standards only apply to commercial products and not hobby stuff etc. Switch-mode supplies are almost ubiquitous in commercial equipment.
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-08-11 15:07
    Prof: Only thing is the price is more expensive than a cheap LM1117 LDO regulator, and more components. So it really depends on the input voltage, or, if you are running on battery. This is why it is not viable on many demo boards. But where you require it, the cost is not an issue, just a simple circuit.

    I had done my research and had missed this ic. I just happened to chat to Peter on the very day I was finalising my research and was going with a different part. Timing was perfect, and I am going to use Peters modules (and my pcb has been changed to take it). Sometimes little modules that can be built in bulk and plug into other pcbs work out cheaper in the long run.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-08-11 16:04
    Peter, what is the value of the inductor and how much are these costing?

    I presume it is a lower uH value than the simple switchers, but it still would need at least 1A current rating?
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2011-08-11 19:43
    Dr_Acula wrote: »
    Peter, what is the value of the inductor and how much are these costing?

    I presume it is a lower uH value than the simple switchers, but it still would need at least 1A current rating?

    This part is 68uH and the reason for this is to do with the wide supply range I am looking at. The part costs me 28c each in 100 quantities from Digikey. Saturation current is 1.3A max which is fine for practically all my needs.

    Also the module is designed with a dual footprint so I can spec a different inductor if need be,
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-08-11 19:53
    Peter,

    That layout is a work of art -- not just engineering! there's not a square micrometer of wasted space!

    -Phil
  • frank freedmanfrank freedman Posts: 1,975
    edited 2011-08-11 20:52
    Peter Jakacki wrote: »
    OK, that's my design tip for the day.

    And a damn fine tip of the day it is:smile:!! One of my potential applications will require running from 120VDC with minimal space and idle current draw (I reeeeaaallllllyyyyyy want to avoid batteries in the device). I was not sure if this were practical, but your little gem has caused a learning function reset!! I may even try my own hand at this.

    Thanks again!!!

    Frank Freedman
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-08-11 21:38
    Nice find on the inductor - and a lot cheaper than the ones the Simple Switchers use.
    I will probably look at getting these made up externally in some volume if the price is right etc.

    If you did do that, would you consider a 3.3V version and a 5V version?
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2011-08-11 21:49
    Dr_Acula wrote: »
    Nice find on the inductor - and a lot cheaper than the ones the Simple Switchers use.



    If you did do that, would you consider a 3.3V version and a 5V version?

    Hi Drac, one of the reasons I switch to 5V first and then 3.3V is to get a cleaner logic supply especially for analog functions, that's why there's an LDO on the module. Anyway, there's a pin available where you can just add your own adjustment resistor to take the voltage up or down to suit.
  • prof_brainoprof_braino Posts: 4,313
    edited 2011-08-13 07:39
    Cluso99 wrote: »
    (and my pcb has been changed to take it). Sometimes little modules that can be built in bulk and plug into other pcbs work out cheaper in the long run.

    that's what I was hoping to hear. Looking forward finding the price and availability.
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-08-13 16:25
    prof_braino: I was referring to another pcb design set (commercial that I cannot divulge - uses 3 props, one setup as a RamBlade with RTC) that can have 24V input.

    However, this pcb module is ideal to power a prop and is simple to wire it up.
  • idbruceidbruce Posts: 6,197
    Peter

    You have been kind enough to help me in the past and I am wondering if you would be willing to provide me with a little more guidance.

    I want to design a new stepper driver with a Propeller on board, that can operate over a wide voltage range. My thoughts are to feed the input voltage into a LM5010A and the output voltage of the LM5010A into a LM2937-3.3 for powering the Propeller chip, meanwhile also bypassing the LM5010A with the input voltage to feed the DRV8825 stepper driver.

    My question is this:

    In section 8.2 Typical Application, of the LM5010A datasheet, an example circuit is shown with an input voltage ranging 6-60V, with an output voltage of 5V. Can this example circuit be used "as is" to feed a LM2937-3.3 regulator for reliably powering a Propeller?

    As always, any effort that you may put forth into answering this question will be greatly appreciated.

    Bruce
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2016-12-21 05:32
    That circuit looks about right but make sure the caps are rated and a lot depends upon the choice of inductor. Remember too that when the Prop is in reset that it draws hardly any current so make sure you have a minimum 500ua load, I like to add a LED power indicator to the 5V rail so that takes care of that too. BTW, I use smaller 3.3 LDOs in SOT89 such as the MCP1700 etc or SOT23 packages normally.
  • LtechLtech Posts: 366
    I use a lot of Murata "OKI-78SR Series" pin replacement of 780X
    Input voltage 7-36Volt max 1,5A exist in 3.3 and 5Volt 85% efficiency.
    We use them on a motorbikes with huge HF transmitters 3-7GHz
    We just put capa's in front and after

    Daniel

  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2016-12-21 08:15
    Ltech wrote: »
    I use a lot of Murata "OKI-78SR Series" pin replacement of 780X
    Input voltage 7-36Volt max 1,5A exist in 3.3 and 5Volt 85% efficiency.
    We use them on a motorbikes with huge HF transmitters 3-7GHz
    We just put capa's in front and after

    Daniel

    For sure those regulators are great off-the-shelf components as are the Recom R-78 series too but they don't come close to the 70V max input rating of the LM5010A which I use in some designs since I made my own tiny modules for these. I'm wary of just sticking any kind of cap on the output though, I may use a 10uF tantalum but I wouldn't load them up too much whereas the input cap is typically a 100uF electro fed from a diode and a series "fuse" resistor. However at the higher input voltages it's easier to use ceramic caps. For that extra bit of input voltage reach I sometimes even use a series zener to drop the voltage a bit more since the input current at that voltage is much lower.

  • idbruceidbruce Posts: 6,197
    edited 2016-12-21 11:11
    Peter

    Thank you for your response and input.
    That circuit looks about right but make sure the caps are rated and a lot depends upon the choice of inductor.

    The Evaluation Board for the LM5010A has a very similar schematic and the App Note(AN-1423) contains a bill of materials. My thoughts are to order the exact same parts as used in the Evaluation Board, or equivalents. For the Evaluation Board they list this inductor: http://www.mouser.com/ProductDetail/TDK/SLF12575T-101M1R9-PF/?qs=VpQJLEvtbIYoNWgTZeTebQ== I am hoping this will be Propeller friendly.
    Remember too that when the Prop is in reset that it draws hardly any current so make sure you have a minimum 500ua load, I like to add a LED power indicator to the 5V rail so that takes care of that too.

    Of course a "LED power indicator" is a must for the type of board I intend to fabricate and the 5V rail is a good location for this LED as you indicate, which does take care of the minimum 500ua load, but doesn't R1 and R2 of that schematic take care of that minimum load?

    It is not necessary to answer that last question, because I will of course be adding the LED as suggested.
    I use smaller 3.3 LDOs in SOT89 such as the MCP1700 etc or SOT23 packages normally

    I will definitely take a look at the MCP1700.

    Thank you for your input Peter. As always you have been very informative and helpful. I hope all is well with you and your family. Good luck with Tachyon V4.... I have been following along with the thread for a while now... Sounds like you have made quite a bit of progress.

    And most importantly, have a very Merry Christmas Peter!
  • tonyp12tonyp12 Posts: 1,950
    edited 2016-12-21 17:12
    Plenty of modules, some even were the substrate is the inductor:
    http://www.mouser.com/Power/DC-DC-Converters/Non-Isolated-DC-DC-Converters/_/N-brvxxZscv7?P=1yxt7boZ1yxt79hZ1yxt79nZ1yxt79pZ1yxt7bdZ1yxt6o1Z1yxt77oZ1yxt7adZ1yxt7a4&Ns=Pricing|0
  • idbruceidbruce Posts: 6,197
    Hey tonyp12... How's it going?

    Interesting link... nice to know that stuff is available.

    Okay... So what is the benefit to buying a module, besides drawing it all up and the soldering?

    The downside would be the voltage limitations for several of the products.

    I just got finished creating the devices for the DRV8825 and the LM5010A in Eagle. After placing those devices into a board, I did a print out and wow those devices are small.

    How expensive is it for a board house to place and solder devices? I realize that is a difficult question to answer, so I am looking for either an "OUTRAGEOUS" or "reasonably priced". :)
  • tonyp12tonyp12 Posts: 1,950
    edited 2016-12-21 18:39
    Diptrace and oshpark.com for small PCB.
    For 0.65mm pitch items get oshstencils.com and you should be able to do a few boards by hand.
    Integrated Current Sense keeps steppers happy.
    http://www.ti.com/lit/ds/symlink/drv8885.pdf

    This simple-switcher have Integrated Synchronous Rectification (saves your from getting a diode) and large 1.27mm pitch
    http://www.ti.com/lit/ds/symlink/lmr23610-q1.pdf


    Get a Stepper driver that is SOIC too, for example:
    http://www.mouser.com/ProductDetail/Texas-Instruments/DRV8803DWR/?qs=sGAEpiMZZMvS/YaWaOF378TkULp/Z%2bZz
    By only using SOIC 1.27mm pitch with 0805 caps and resistors, easy stuff to do by hand.
  • idbruceidbruce Posts: 6,197
    Tony

    Instead of hijacking Peter's thread and going way off subject, I would be more than happy to discuss all of these issues within the thread I started for the stepper driver, which can be found here: forums.parallax.com/discussion/165669/eagle-complex-device-and-vias-stepper-driver-discussion

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