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Related

RG1 1.8v regulator

Former Member

Ok, so in a different thread I threatened to remove RG1 and do some current measurements on it's output after seeing those thermal images that show it's not generating any heat...

 

Well, I did it tonight. Some photos here: https://picasaweb.google.com/selsinork/RPi18v

 

The jumper pins in the output let me either just put a jumper on and verify the Pi boots ok, or wire a multimeter in series to get some current readings.

 

The results were interesting to say the least. I had to go back and check I was reading the multimeter correctly, that it wasn't broken etc.

 

On initial power up I see a negative current for a second or so which then reverses to about 0.5mA (yes half a milliamp, that's not a typo) for a few seconds while we get the first sd-card accesses. Once we're booted and sitting at the login prompt the current reading fluctuates from around 0.001mA to maybe 0.04mA. 

 

I'm using the 40mA range on a decent Fluke multimeter, so I've no reason to doubt the results. There's obviously going to be some inaccuracy down at that level due to length of meter leads etc, but the result is fairly clear.  You'll understand why I was checking the meter was working and I was reading it correctly though image

 

 

So from there onto the next test, lets try completely disconnecting RG1 and see if the Pi boots while using the LAN9512 1.8v 'output'.  Yes it does! 

 

I think that's reasonably good indication that jamodio got it spot on, the lan9512 shouldn't be connected to the 1.8v plane and it's heat problems are going to be largely due to supplying current on it's 1.8v filter pin that it was never designed to do.

 

So anyone willing to pull RG1 off a Pi and verify my results ?

  • in reply to rew

    Reminds me of the "classic" text string for serial communications (you can add the lower case version obviously)

     

    THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG 1234567890

     

    http://en.wikipedia.org/wiki/The_quick_brown_fox_jumps_over_the_lazy_dog

     

    -J

  • Thanks guys for the ideas for testing the usb issue.

     

    I think the network ping is some thing i will look more into but the serial testing is an good idea but i think it will make my testing to complex and need more gear in the setup, i think it is better to keep it simple for this testing or i will never have it done.

     

    In fact at the time i am testing the switch mode psu modules i have to find what of them is best will do the 1.8v and 3.3v at 50-150mA, but the ones i have now dont seems to be very efficiency at that small load..

     

    The module i am testing is this one: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280939678549

     

    here you can see the efficiency of one module i am testing now and it seems not to be very efficiency at loads in the low end, so if the load from the RPI is only 50-150ma then the efficiency is only 29-55% and that is not good.

     

     

    DC Load(A)               Efficiency(%)           

    0,0100                        7,2210

    0,0500                      29,4073

    0,1000                      45,4059

    0,1500                      55,5899

    0,2000                      62,4374

    0,2500                      67,5141

    0,3000                      71,2567

    0,3500                      74,2060

    0,4000                      76,5965

    0,4500                      78,5389

    0,5000                      80,1118

    0,5500                      81,4908

    0,6000                      82,6600

    0,6500                      83,5954

    0,7000                      84,4475

    0,7500                      85,1550

    0,8000                      85,7698

    0,8500                      86,2674

    0,9000                      86,5859

    0,9500                      86,6444

    1,0000                      86,9425

     

     

    So i am in the need to find an better switch mode supply, do you know ones that i can get easly ?

     

     

    I have got some LMZ10501 but they are one the chips and no board so i have to build them up first, but i think they will be alot better for this low load.... but damm they are small.

     

     

     

    Thomas

  • in reply to Former Member

    Yeah. In first approximation, many switched regulators have a constant current "loss" and then an efficiency for "infinite" current. In your case the "limit" efficiency is about 88%. The constant current can be deduced from your measurements, but I'm too lazy to figure it out.

     

    You should be able to get an efficient switching powersupply with modern chips. The cheap ones on ebay are built around (copies of?) ancient chips that "work, but are not that efficient".

     

    I just went to "ti.com", and then clicked that I want a 4.5-5.5 input, 1.8V output, 150mA powersupply. Then I clicked on one of the "most efficient" designs, and got one that should be affordable at "bom cost $1.85".

     

    In single numbers they cost about EUR 2,- This sounds "doable". I'll see if I can make a small test-PCB for one of these guys this week. (hihi: The 1.8V output circuit is the reference design on page 1 of the datasheet).

     

    To improve efficiency, it that's what you're after, it would pay to make a 1.85V switcher, and leave the LAN9512 connected to the 1.8V plane. Hopefully that would switch off most of the internal regulator in the '9512....

  • in reply to morgaine

    Hey Morgaine,

    As a somewhat related question. . . posible for you to suggest an affordable soldering iron with a small tip-to-grip ratio? Price range around $125 or so? Everything I come across is beaucoup bucks! I have a "hobbiest" iron from Adafruit but don't think it's going to work for me. Since I'm quite interested in this stuff I should invest in something I can use for eons..

    Thanks as always

    Peg

  • in reply to Former Member

    Peg,

    Check out Aoyue. http://www.aoyue.com/en/ArticleShow.asp?ArticleID=372

    For a little over $125 you might be able to get a combination station that also does hot-air. I have the just-hot-air station from them. (and the weller)

  • in reply to Former Member

    I don't know of one yet, but I'm definitely in the market for one because under 14X binocular magnification it's really hard to control an iron with a long tip.  Currently looking through jamodio's links.

     

    Addendum:

     

    • The iron that comes with Adafruit's Hakko FX888 Soldering Station seems to be 190mm long without cord, and the tip looks kinda long.
    • Newark's Tech Data Sheet link for the Weller WES51 is currently down for me, I'll check again later.  On Farnell UK, no such model, might be US-only.
    • Weller have a "micro" range WHS-M,  http://uk.farnell.com/weller/whs-m-uk-eu/soldering-staion-40w-230v/dp/1729967 , which looks very small, but I can't see the actual tip length specified.

     

    General comment about Weller pricing ... ouch. image  It's clearly industrial pricing, hard to justify for very occasional use.

     

    Morgaine.

  • Hi

     

    I am in the process on testing how little power the RPI can use and what heat there is, so i will just share some small limit results with you.

     

    In the test setup i have:

    Disconnect the LAN9512 from the main 1V8 power rail on the board.

    Add caps to te LAN9512 as the SMSC pdf says

    Removed the RG1

    Removed the RG2

     

    I have then connected external power supplys for the 1V8, 3V3 and 5V0 Rail and on each rail there is an volt and amp meter so i can see how many V and mA there is used on each rail.

     

    Here is when the RPI is just power up and is idle

    Rail 1V8          1,8000V * 0,06338A = 0,114084W

    Rail 3V3          3,3400V * 0,02460A = 0,082164W

    Rail 5V0          4,9900V * 0,04605A = 0,022979W

    Idle mode total = 0,426038W

     

    Here is when the RPI calc PI

    Rail 1V8          1,8000V * 0,06351A = 0,114318W

    Rail 3V3          3,3300V * 0,02710A = 0,090243W

    Rail 5V0          4,9200V * 0,07973A = 0,392272W

    RPI calc PI total = 0,596833W

     

    Note: the reason it is the 5V0 rail there is having higher mA when calc PI is because i have not removed the RG3 from the board, the RG3 is feed the CPU with 2V5 from the 5V0 rail.

     

     

    wow this is much lower then i was thinking it was using and it seems there is alot to save with an very good switch mode regulator..

     

     

    So this was just to share some test details with your guys.

     

     

    Tooms

  • in reply to morgaine

    I found other discussions regarding this question. Sorry to have jumped in to the wrong discission. . . I'm going to check into the chinese market. Thanks for the suggestions. I'll let you know what I come across for soldering irons. The "re-work" stations have me confused. . .like what would I ever need a hot air gun for??

    Best,

    Peg

  • in reply to Former Member

    Tooms wrote:

     

    wow this is much lower then i was thinking it was using and it seems there is a lot to save with a very good switch mode regulator..

    Thank you for sharing your measurements.  Those numbers do seem low, but calculating pi probably doesn't use much RAM.  I believe the power consumption goes up a lot with:

     

    1.  Large computations that don't fit in cache, so there's lots of DRAM activity.  Large compiles are good candidates.

     

    2.  Heavy GPU use such as 3-D graphics and video decode.  Those would also have a lot of DRAM traffic.  I don't know how much HDMI adds in when active.  I know my RasPi draws more current when X Windows comes up.

     

    3.  Ethernet, which has 50 Ohm pull-up connected to +3.3V.  USB probably uses a lot when it's driving.

     

    I remember my board being quite a bit warmer with Ethernet hooked up, so I typically just connect it for a few seconds to get the correct time and then leave it disconnected.