[time-nuts] FE-5680A Breakout board
attila at kinali.ch
Sun Jan 15 05:09:08 EST 2012
On Sun, 15 Jan 2012 00:56:05 +0000
"gonzo ." <cadbloke at hotmail.com> wrote:
> On the schematic the inputs are listed as "supply" (ie. "+15V_SUPPLY" and "+5V_SUPPLY"), where as the outputs of the regs are marked with their actual voltages.
> The boards silk screen on the other hand lists the inputs as 7V and 17V.
Ah.. ok.. overlooked that.
> In my original post I said I'd used the LM317 from the Eagle library, but infact use the pin compatible LM1084 (Eagle doesn't know about the LM1084).
> The LM1084 is a 5A device (vs 1.5A:LM317) with 1.5V LDO (vs 2.5V:LM317), so 17V is an acceptable minimum input.
> Heatsinking of the LM/TS/AMS1117 is not generious and it does run hot when SJ1 is shorted and the board is running with a single supply (15V input to the 5VReg).
> I have added more heatsink ares to the V1.1 board, but the '1117is rated to 800mA and is only loaded to 10% so I don't think it is a problem.
Please be aware of the fine print: These chips can handle that much current
if and only if you can keep the junction temperature below the rated
maximum (usually 130-150°C). This means, you have to be able to disipate the
approx 1W while keeping the case temp below 120°C. Natsemi/TI say that their
SOT-223 case has a thermal resistance of 10°C/W (junction-case), so this
should be easily done if you have enough copper around or have a pad where
you can solder a small metal fin on (i guess any metal larger than 1cm^2
should be enough). Fortunately the 1117 has a themal shutdown that will
prevent it from frying.
And also a little warning here: There are many companies producing the "same"
device, but the specs have little differences, especially when you get
the device to its limits. In this case, when you let the *1117 run very
hot, you should keep in mind that different versions behave differently.
> It is worth remembering that the boards I'm offering are simply the left overs from my own use (V1.0 board at least) and was never intended to be fully idiot proof. Fortunatly, this list seems to be an idiot free corner of the internet
*g* not 100% idiot free, but the ratio of people who can think is very high :-)
Why does it take years to find the answers to
the questions one should have asked long ago?
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