I should have made it more clear, but there are no switching regulators in the same package as the linear regulators available on the market, otherwise someone would have done it months ago. Basically I made a PCB that "breaks out" a switching regulator and the necessary capacitors/inductor to DPAK/SOT-223 footprints. That said, the 3.3V regulator is a TI TPS62291, and the 1.8V regulator is a Murata LXDC2HL18A.RaTTuS wrote:...and what ones did you buy [link for the lazy]
Replacing the regulators is actually pretty easy, the trick is to snip the leads with a wire cutter, then apply enough heat to the metal tab. Designing, depanelizing and assembling the modules, on the other hand, is quite a bit of work.alexeames wrote:Was it hard to do?
Correction -- the metal tab is actually the output node, but your method would still work. I imagine it would be easier too since there's less of a size constraint. I did it the way I did it mainly for the challenge.cowpat wrote:I don't have any SMT tools - but i do have a nice pair of sidecutters. Other than cosmetic reasons, why not just cut/lift the legs and leave it in situ? - the big metal that needs the heat is just 0v isn't it?
You can see that better now. I could have sworn Gert said something at one time about a drop-in replacement? Was it in the power thread or somewhere else?
Impressive!azerty wrote:Basically I made a PCB that "breaks out" a switching regulator and the necessary capacitors/inductor to DPAK/SOT-223 footprints.
That regulator could be put in place of the 5v (RG2) reg. It can take an input voltage up 30v and puts out [email protected] I do have some adjustable switching regulators on seperate boards. But this would be a lot smaller footprint and just look better all around. It is only slightly bigger than a 7805.AndrewS wrote:Might be cheaper / easier to use separate 12V->5V and 5V->3.3V regulators?
Ah so you want me to use the easy old LM2596 adjustable regulator boards, that I already have, instead of taking the iron to one of my Pi's! So where in the heck is the fun of that? Hack it together with soldered wires and boards instead of the Elegant, plug it into the stock Micro USB (albeit it will be 12v instead of 5v). And at the miniscule cost of like 27% the total cost of the board? Shame AndrewS, Shame!AndrewS wrote:Ahhhh, the old size vs. cost challenge...
You should feed the RPi with 5V, or else you will need another 5V reg for the USB ports.Lob0426 wrote:@ Douglas W. Jones: I was one those people. RG2 is indeed 3.3 volts. I ordered a 5v (RECOM R-78C5.0- 1.0) DC/DC converter to supply RG2 with 5v. I also ordered (RECOM R-78C3.3- 1.0) to replace RG2. I will have to build a board, then wire it to the RasPi. I plan on putting 12v into that board. The R-78C3.3 will work to replace the Linear with a switching, but you then have no 5v for your USB.
That is the crux of the problem with the RasPi. It relies upon the the power suply for way too much. The parts I quoted above have ripple somewhere between 240 to 350Hz. That is why I plan to mount them off board, so I can put on the capacitors to calm the ripple. I will mount a R-78C5.0- 1.0, 5v and a R-78C3.3- 1.0, 3.3v to the board and feed both 12V from a wall wart. The LM2596's seem to be pretty stable and would make a good alternative to taking a soldering iron to the RasPi itself for most people. I also am running heat sinks on RG2, SoC and the LAN9512. I want to run the a wireless router and the RasPi from the same power source(12v). My first attemp will be with the LM2596. I will experiment from there.carlosfm wrote:You should feed the RPi with 5V, or else you will need another 5V reg for the USB ports.Lob0426 wrote:@ Douglas W. Jones: I was one those people. RG2 is indeed 3.3 volts. I ordered a 5v (RECOM R-78C5.0- 1.0) DC/DC converter to supply RG2 with 5v. I also ordered (RECOM R-78C3.3- 1.0) to replace RG2. I will have to build a board, then wire it to the RasPi. I plan on putting 12v into that board. The R-78C3.3 will work to replace the Linear with a switching, but you then have no 5v for your USB.
Presently I use a 12V switching PSU, which I have tweaked here and there to reduce the noise, then an RC filter feeding a 7805, which has a big heatsink, then it enters the Pi though a 2.5mm transformer plug (I don't like the Micro USB plug, it was a bad idea IMO, it doesn't handle the necessary current), then a ferrite bead directly to TP1 (which bypasses F3).
The USB polyfuses were replaced with SMD ferrite beads and then 10uF ceramics to ground, on the power pins of each USB output.
These 10uF ceramics were removed from the analog output, because ceramics are some of the worst types for coupling caps (the other ones are tantalum).
The analog outputs have proper non-polarized 10uF electrolytics.
I also have heatinks on the CPU, the network chip, and RG2.
Why all this?
Well, in my book you need a stable, silent PSU, and good capacitance where needed.
The 7805 and the other onboard regs are not brilliant, far from that, but switching regulators are usually noisier - it very much depends on the implementation, and space is at a premium here.
Also, cool running improves stability and long time reliability.
I have my Pi running stable at 1100Mhz (CPU), 500Mhz (GPU) and 550Mhz (Ram).
This would not be possible with a lowsy mobile phone charger - those have copious amounts of ripple and the output voltage is not stable.
If you replace both RG1 and RG2 with switching regulators, then you should also make RG1 take its input from 5V instead of 3.3V. There are two reasons for this:Lob0426 wrote:... The 500ma should be more than sufficient especially since RG1 would be replaced also.
I read that entire thread, and the second thread it referenced. In summary, there is a genuine and acknowledged design error in the Pi. Some boards have the LAN9512 output voltage just epsilon higher than RG2, so the LAN chip runs very hot, supplying the 1.8V power to the entire Pi. Other boards have RG2 providing epsilon more volts, so it powers the Pi and the LAN chip runs cool.Tooms wrote: The guys of this thread has discovered that the RG1 1.8V LDO is not having any load ...
This is an design error because the 1.8v pins on the LAN9512 is design to the caps and not power external things.
He included a photo and he said that his Pi worked no worse after making this change than before, along with measurements that make it clear that he successfully isolated the two 1.8v supplies from each other.Carefully, I cut the circuit traces from pins 15 and 38 on LAN9512 and the 1.8V side of C29 to the vias. I then very carefully soldered some wire between these three points. This more closely resembles how the circuit should be (minus the 100nF caps). (The 9512 reference design says 4u7 should be by pin 38 btw)
Thanks for you reply:Douglas W. Jones wrote:If you replace both RG1 and RG2 with switching regulators, then you should also make RG1 take its input from 5V instead of 3.3V. There are two reasons for this:Lob0426 wrote:... The 500ma should be more than sufficient especially since RG1 would be replaced also.
a) This lowers the current through RG2, which currently supplies RG1. That design is sensible with linear regulators, but with switchers, it lets RG2 work closer to the "sweet spot" for the efficiency of 5V to 3.3V switching regulators, which is around 100mA for a regulator with maximum current capacity of 500mA.
b) RG1 will have about equal efficiency whether powered from 5V or from 3.3V. Power it from 5V, and you don't pay an efficiency penalty for dropping 5V to 3.3V first. Run RG1 at perhaps 85% efficiency, instead of running RG1 at 85% in series with RG2 at %85 (for a net efficiency closer to 70% on the output of RG1.
I suspect the net gain is marginal, but it makes sense to do it right.
Another thing to note about the bucking switching regulator ICs I've looked at. They all have overtemp and overcurrent protection built in -- that is, the regulator will turn off if it gets too hot, and it will turn off if the output current goes too high. If you put one of these regulators on the input to a system that's powered, for example, by 10 to 18 volts, does that eliminate the need for a fuse?
-- Doug Jones
-- [email protected]