Shop OBEX P1 Docs P2 Docs Learn Events
NeoPixel Christmas Ornament (was "Prop Mini power supply") — Parallax Forums

NeoPixel Christmas Ornament (was "Prop Mini power supply")

David BetzDavid Betz Posts: 14,516
edited 2014-12-24 09:59 in Propeller 1
I just ordered a Prop Mini to use with my LED Christmas tree ornament project. I also have an AdaFruit RGB LED ring with 16 LEDs that I'm hoping to drive from the Prop Mini. I looked at the data sheet for the Prop Mini and it says that VIN is supposed to be "regulated 6.5–12 VDC @ 1A". Does this mean I can't just use a 9V wall wart? Why does the power need to be regulated if there are on-board regulators on the Prop Mini? Also, it looks like I may need to make sure the LEDs are not at full brightness because the Prop Mini 5V regulator says it can only provide 1A including whatever is consumed by the 3.3V regulator that powers the Prop itself. The data sheet says I should not draw more than 600ma from the 5V supply. Am I taking a risk here of overloading the 5V regulator?
«1

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2013-12-12 14:42
    Unregulated wall warts can put out much higher than their stated voltage when the current demand is less than the stated current. Your "9V" unit may, in fact, put out more than 12V without a decent load. The datasheet, by stating the "regulated" requirement, is simply preventing damage from a supply that could put out more than 12V, even though the faceplate voltage is less.

    -Phil
  • David BetzDavid Betz Posts: 14,516
    edited 2013-12-12 14:58
    Phil Pilgrim (PhiPi) wrote: »
    Unregulated wall warts can put out much higher than their stated voltage when the current demand is less than the stated current. Your "9V" unit may, in fact, put out more than 12V without a decent load. The datasheet, by stating the "regulated" requirement, is simply preventing damage from a supply that could put out more than 12V, even though the faceplate voltage is less.

    -Phil
    I guess I don't understand this. If I use a regulated wall wart then presumably there is a regulator inside of it. Why doesn't that regulator suffer the same problem as the one on the Prop Mini board? Is it likely to be a better quality regulator that can handle a wider range of input voltages?
  • Don MDon M Posts: 1,652
    edited 2013-12-12 15:37
    David do you own a digital volt ohmmeter? If not I would suggest you put that on your Christmas list. One that also measures current would be a good choice. Good investment that will allow you to discover the answers to your questions here.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2013-12-12 15:54
    David Betz wrote:
    Is it likely to be a better quality regulator that can handle a wider range of input voltages?
    Dunno about "better quality." But yes, some regulators are designed for wider input ranges than others. There's also the issue of heat dissipation when the input/output differential is high. A smallish regulator without a heatsink is especially vulnerable to overheating under such circumstances.

    -Phil
  • LawsonLawson Posts: 870
    edited 2013-12-12 16:22
    David: Have you looked in the Prop Mini schematic and then pulled up the datasheet for the regulator it's using? That will tell you the actual limits of the regulator. Parallax often de-rates the input specifications of boards they make so the boards can handle every corner case. (i.e. not melt at 12VDC and 600mA) With a heat-sink upgrade the regulator can probably handle a good bit more. I've found that a copper tab (old penny?) or coil of heavy copper wire soldered to the regulator tab make good heat-sinks.

    Marty
  • David BetzDavid Betz Posts: 14,516
    edited 2013-12-12 16:41
    Lawson wrote: »
    David: Have you looked in the Prop Mini schematic and then pulled up the datasheet for the regulator it's using? That will tell you the actual limits of the regulator. Parallax often de-rates the input specifications of boards they make so the boards can handle every corner case. (i.e. not melt at 12VDC and 600mA) With a heat-sink upgrade the regulator can probably handle a good bit more. I've found that a copper tab (old penny?) or coil of heavy copper wire soldered to the regulator tab make good heat-sinks.

    Marty
    Thanks for the suggestion. I'll try adding some sort of heat sink.
  • David BetzDavid Betz Posts: 14,516
    edited 2013-12-12 16:41
    Don M wrote: »
    David do you own a digital volt ohmmeter? If not I would suggest you put that on your Christmas list. One that also measures current would be a good choice. Good investment that will allow you to discover the answers to your questions here.
    I have one. I guess it's time to get it out!
  • David BetzDavid Betz Posts: 14,516
    edited 2013-12-12 16:48
    Lawson wrote: »
    David: Have you looked in the Prop Mini schematic and then pulled up the datasheet for the regulator it's using? That will tell you the actual limits of the regulator. Parallax often de-rates the input specifications of boards they make so the boards can handle every corner case. (i.e. not melt at 12VDC and 600mA) With a heat-sink upgrade the regulator can probably handle a good bit more. I've found that a copper tab (old penny?) or coil of heavy copper wire soldered to the regulator tab make good heat-sinks.

    Marty
    I just looked at the schematic and it says the Prop Mini uses a LM2937-5.0 regulator. When I looked that up the references I found said it was a 500ma regulator but the Prop Mini page says it has a 1A 5V regulator. Is the schematic wrong?
  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2013-12-12 17:27
    David, the schematic is calling out the LM2937, but the part on the board is an LM2940 which can push 1A. The part marking is L53B and on the LM2940 datasheet, that equates to an MPN of "LM2940IMP-5.0/NOPB". The LM2937 would have a marking of L73B.
  • David BetzDavid Betz Posts: 14,516
    edited 2013-12-12 17:32
    WBA Consulting wrote: »
    David, the schematic is calling out the LM2937, but the part on the board is an LM2940 which can push 1A. The part marking is L53B and on the LM2940 datasheet, that equates to an MPN of "LM2940IMP-5.0/NOPB". The LM2937 would have a marking of L73B.
    Okay thanks for checking. I don't have the Prop Mini yet so all I had to go by was the schematic.
  • LawsonLawson Posts: 870
    edited 2013-12-13 10:51
    WBA Consulting wrote: »
    David, the schematic is calling out the LM2937, but the part on the board is an LM2940 which can push 1A. The part marking is L53B and on the LM2940 datasheet, that equates to an MPN of "LM2940IMP-5.0/NOPB". The LM2937 would have a marking of L73B.

    *rant* and this is why I wish the full 2-3 line part number, logo, and date code was micro-printed on all surface mount packages. (not just the bigger ones) Having something like "L53B" on a little SOT-23 package is far less useful for than if they micro-printed "LM2940" "IMP-5.0" "NOPB" on the package. (how many parts are labeled with "L53B"?) */rant*

    Marty
  • PublisonPublison Posts: 12,366
    edited 2013-12-13 11:18
    Dave,

    I would get a Radio Shack regulated PS. I like the:

    http://www.radioshack.com/product/index.jsp?productId=3875403

    1     amp and adjustable voltages. The regulated PS from RS have been very good for the past two years.

    I have four such PS and have performed flawlessly.

    Make sure to get the adapter for the Parallax products:

    http://www.radioshack.com/product/index.jsp?productId=3807939

    J    im
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2013-12-13 11:35
    As an addendum, do not use any wall wart that's labeled with the word "charger." Those typically are not only unregulated, but unfiltered as well.

    -Phil
  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2013-12-13 14:56
    Lawson wrote: »
    (how many parts are labeled with "L53B"?)

    From TI, only one. That's why many companies don't seem to think that a part marking search database on their website is important. TI, however, does have one, but it is hard to get to unless you know where it is at:

    TI Home > Analog and Mixed Signal Home > Special Function Home > Design Resources > TI Packaging Info > Part Marking Lookup

    . Google can only do so much for part markings. I run into this exact issue at work frequently when we are building prototypes with very little documentation or when programming our AOI machines. It becomes very difficult to confirm that the part you have matches the mile-long MPN that you purchased to.
  • TubularTubular Posts: 4,702
    edited 2013-12-13 16:01
    David,

    For driving these led pixels/strips, I've been applying 5v to the propeller board (generally the prop proto board, but should work with mini too). You apply 5v to the Vin, and to the led strip directly (not via the 5v regulator). The 5v regulator will "drop out" and put out something like 4.3v, still enough for the 3v3 LDO regulator to work with, although I haven't tested up to 8 cogs simultaneously with this arrangement.

    The advantage of this is there is an ever expanding range of USB (~5v) wall warts, battery packs. Here it is easy and cost effective to purchase switchmode wall warts up to 5v 4 amps. After that you can get "laptop style" power supplies up to 5v 10A (Adafruit), and beyond that you're looking at PC atx supplies. The key point is get a 'switchmode' power supply as the regulation is "more rigid" (maintains an even 5v under any load condition) than traditional plugpacks.
  • David BetzDavid Betz Posts: 14,516
    edited 2013-12-13 19:32
    Tubular wrote: »
    David,

    For driving these led pixels/strips, I've been applying 5v to the propeller board (generally the prop proto board, but should work with mini too). You apply 5v to the Vin, and to the led strip directly (not via the 5v regulator). The 5v regulator will "drop out" and put out something like 4.3v, still enough for the 3v3 LDO regulator to work with, although I haven't tested up to 8 cogs simultaneously with this arrangement.

    The advantage of this is there is an ever expanding range of USB (~5v) wall warts, battery packs. Here it is easy and cost effective to purchase switchmode wall warts up to 5v 4 amps. After that you can get "laptop style" power supplies up to 5v 10A (Adafruit), and beyond that you're looking at PC atx supplies. The key point is get a 'switchmode' power supply as the regulation is "more rigid" (maintains an even 5v under any load condition) than traditional plugpacks.
    That's a good idea. I'll try that since even the 1A 5V regulator on the Prop Mini isn't really enough for my 16 RGB LED ring that claims it can draw up to 1A.
  • TubularTubular Posts: 4,702
    edited 2013-12-13 21:53
    Yep. I've been running that way successfully since July. It would be good to know if it works with the mini too. Unfortunately I don't have one to try. Even though the 5v regulator on the mini may be rated for up to 1 amp, in practice without fan forced cooling that little area would heat up very quickly and the regulator would shutdown (temporarily, most likely).

    One thing about the WS2812B's ("neopixels") they don't tell you... the (WS2811) electronic driver inside each LED usually takes about 1mA at 5v. However that supply current "takes off" on an exponential rise if you supply them above 6 volts or so, and is really quite significant by 7 volts. It's consumed even when the led is "off" (ie set to 0,0,0 intensities). I don't think Adafruit should advertise them as operating off 4-7v, really.

    That current must be distributed as heat and may be putting parts of the driver under stress it's not used to dissipating.

    Edit: I like your idea of the rings to decorate the tree. It'll look great. Make sure you get some pics for us. Adafruit may be interested in them too
    pdf
    pdf
    ws2812b led characteristic curves.pdf
    6K
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-12-14 04:52
    I think you should consider this in terms of heat on that Propeller Mini. I also have one and can see from a heat buildup standpoint why it is rated at 600ma 5v even though the regulator might be a 1 amp capable device.

    If you are going to get the most out of a regulator, you have to include adequate heat removal and the mini is small.. so the regulator is derated. It might also be the packaging in a surace mount device that requires the derating as well.


    As far as the regulated power supply....
    Nearly all the wall warts I can buy these days are regulated. It is my old ones that sit in my junk box that are unregulated.

    Nonetheless, I have abandoned the use of 9V supplies in favor of 7.5V supplies. They just produce that much less heat on the Mini, so everything runs cooler and likely will last longer.

    If I need additional 5 volts, I might have a second regulator board, aside from what is on the Mini provide that power to other devices. I often prefer 1.5 amp to 2.0 amp 7.5 wall warts for my jump from 120VAC... so there is extra power to use as demanded. I know this adds more wiring clutter, but building the tiniest of tiny tends to be a poor design approach. Work up your Power budget based on real requirements, ponder what is the best way to distribute power so that the device will last a long time, and build accordingly...even if it is larger.

    Heater gets very annoyed at me just because I think the Raspberry Pi took the tiniest of tiny design approach as has a strangled power distribution. To get the USB keyboard and mouse to work right, you end up with even more clutter in an outboard supply. It should of had about 2 amps of available USB power from the start... that is why I strongly prefer an alternative.. everything plugs into one board with one power source. Of course it is twice as large, I don't have a nest of wires and adapters to make it right.... just one board that is tidy.
  • David BetzDavid Betz Posts: 14,516
    edited 2013-12-14 05:06
    Loopy Byteloose wrote: »
    I think you should consider this in terms of heat on that Propeller Mini. I also have one and can see from a heat buildup standpoint why it is rated at 600ma 5v even though the regulator might be a 1 amp capable device.
    The data sheet for the Prop Mini says that the 5V supply should be limited to 600ma because the 3.3V regulator can draw up to 400ma so I think they expect that you can get a full 1A out of the 5V regulator.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-12-14 05:14
    No, I would say that they think you can get 200ma out of the 1a regulator because it is in a tiny SMD on a board without a heat sink.

    Parallax buys these regulators in reels. There is no reason to buy more inventory when a 500ma regulator and a 1 amp regulator are about the same price. But it is the thermal design context that decides the actual maximum.

    In the old days, the 7805 would just melt the solder and slide off a BasicStamp when you demanded too much power for the heat budget. But the newer votage regulators just have a thermal shutdown to prevent that. Over 600ma, you may risk having mysterious shut downs.
  • RS_JimRS_Jim Posts: 1,766
    edited 2013-12-14 05:16
    Publison wrote: »
    Dave,

    I would get a Radio Shack regulated PS. I like the:

    http://www.radioshack.com/product/index.jsp?productId=3875403

    1     amp and adjustable voltages. The regulated PS from RS have been very good for the past two years.

    I have four such PS and have performed flawlessly.

    Make sure to get the adapter for the Parallax products:

    http://www.radioshack.com/product/index.jsp?productId=3807939

    J    im
    Pick those up in a store and the adaptaplug is free.
    Jim
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-12-14 05:22
    I can see that you want to read 5v at 600ma plus 3.3v at 400ma indicates that the 5V regulator is working at a full 1 amp.

    But the truth is that i have to dig up my Mini, take a close look at the 5v regulator, download the pdf, and read in detail the information about its thermal properties in the same SMD and in the same installation context to be sure 1 amp will work.

    So I am being conservative. I learned with the BS2 to not expect the 5VDC to provide outboard power to all and everything I wanted to attach. It just won't work out well.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-12-14 05:30
    I located the schematic for the MINI online and it specifies an LM2937-5.0 voltage regulator.... which has a maximum output ability of 500ma. So it seems the 600ma is a typo, and there is only 100ma of headroom after providing 400ma to the 3.3v regulator, an LM2937-3.3.. also rated at 500ma tops.

    Sorry but I feel you are being too optimistic. You really have to take the thermal situation into account, always.
  • Don MDon M Posts: 1,652
    edited 2013-12-14 06:18
    I find the USB type smart phone chargers make a great supply for projects. You can find some rated anywhere from 500mA to 1A @ 5VDC. I look for them at garage sales for cheap and scarf them up when I can. Usually $1.
  • David BetzDavid Betz Posts: 14,516
    edited 2013-12-14 06:29
    Loopy Byteloose wrote: »
    I located the schematic for the MINI online and it specifies an LM2937-5.0 voltage regulator.... which has a maximum output ability of 500ma. So it seems the 600ma is a typo, and there is only 100ma of headroom after providing 400ma to the 3.3v regulator, an LM2937-3.3.. also rated at 500ma tops.

    Sorry but I feel you are being too optimistic. You really have to take the thermal situation into account, always.
    I checked with the support people at Parallax and they said they are now using the "LM2940IMP-5.0 from Digikey, which has a 1A output." They are in the process of updating the schematic to reflect this change and also some unspecified change in the EEPROM.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-12-14 07:03
    David Betz wrote: »
    I checked with the support people at Parallax and they said they are now using the "LM2940IMP-5.0 from Digikey, which has a 1A output." They are in the process of updating the schematic to reflect this change and also some unspecified change in the EEPROM.

    I guess you see what is going on... I generally try to take a look at what is actually installed on the board and work from there to avoid typos and writers that are not 100%. But in this case, when I look on the Propeller Mini in my possession, I have a 326n-L5Jb and a 34EK-L69B. So it is really difficult to gain any assurance that I have LM2937 or LM2940 regulators.

    You may be able to squeeze 1 amp out of the on-board 5 volt regulator, but it still depends on thermal conditions of both the SMD and the heat disapation, NOT the Absolute Maximum Rating of the part.

    http://www.ti.com/lit/ds/symlink/lm2940-n.pdf

    Pages 14, 15, and 16 of the lm2940-n.pdf explain a rather involved proceedure to figure this out. But I do standby the basic ideas - smaller components that are surface mounted with less than optimal heat sinks are NOT going to provide the part's Absolute Maximum Rating.

    In addition, the higher the input voltage... the greater your heat problem might be. A 7.5 Volt power supply would still be a better choice than 9.0 V.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2013-12-14 09:31
    The device is rated for "1A", but my expectation would not be to wring every bit of that out in this instance.
    YMMV.

    The datasheet's model is 1 sq in of 1 ounce copper for heatsinking.
    The Mini, in all, might be 1 1/2 sq in. How much of that area fills the bill, let alone its thickness, I know not.

    I see on the Mini's schematic that the 3V supply is sourced from the 5V, so demand from the 3V device (however negligible) has to be included in the 5V & IIN calcs.

    http://www.ti.com/lit/ds/symlink/lm2940-n.pdf
    http://parallax.com/sites/default/files/downloads/32150-Propeller-Mini-RevA-Schematic.pdf

    Wall-packs are, typically: a transformer with a FWB (rectifier) and a smoothing cap.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2013-12-14 09:56
    On point missing from this discussion is the input voltage to the regulator, It's the input-output differential, times the current, that determines the heat dissipation, not just the current alone. If the input voltage to the LM2940 is only 5.5V, say, the heat dissipated at 1A would only be 1/2W. OTOH, with an input voltage of 9V, the same part would have to dissipate 4W -- unlikely without additional heatsinking.

    -Phil
  • LawsonLawson Posts: 870
    edited 2013-12-14 11:20
    WBA Consulting wrote: »
    From TI, only one. That's why many companies don't seem to think that a part marking search database on their website is important. TI, however, does have one, but it is hard to get to unless you know where it is at:

    TI Home > Analog and Mixed Signal Home > Special Function Home > Design Resources > TI Packaging Info > Part Marking Lookup

    . Google can only do so much for part markings. I run into this exact issue at work frequently when we are building prototypes with very little documentation or when programming our AOI machines. It becomes very difficult to confirm that the part you have matches the mile-long MPN that you purchased to.

    Can you post a direct link to the part marking lookup? I can't seem to find it via your progressive links or a few quick searches of TI's web-site. (grrr... why hide this info????)

    Marty
  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2013-12-14 11:32
    My bad, here ya go:

    http://focus.ti.com/general/docs/partmarking/partmarkinghome.jsp
Sign In or Register to comment.