[En-Nut-Discussion] Hardware and fuse info

[Bas Nedermeijer]

Hi Harald,

<snip>

> At egnite the boards are automatically tested up to 12V DC,
> measuring the current.
>
> I'll explain the Ethernut 2 power supply in detail, as there
> are obviously uncertainties and many people asked related
> questions in the past. In general, the same applies for
> Ethernut 1. But not for Ethernut 3, which has an advanced
> switching regulator with a wide input range of 5-24V.
>
> Please check the schematic page 4, starting at the barrel
> connector J2. This power supply input is connected via AC1/2 to
> JP3 (on page 3), which allows to alternatively supply the board
> via the two spare wire pairs of the Ethernet TP cable (10/100 MBit
> needs  two pairs of the eight wires only). By default, jumpers at
> JP3 (located near the Ethernet connector) should be removed.
> Ethernut 2 doesn't support standard power over Ethernet. It's
> more like poor man's PoE and requires a special injector box.

Yes, these are removed.


> Back to page 4 of the schematic. Power then flows through the
> fuse (1A, fast acting, LittleFuse Part # 0453 001) and passes
> D3. This is a bidirectional Transil Diode, which is used as
> an overvoltage protection. If the supply raises above about
> 15V, this diode shorts the power supply within very short time.
> As a result the fuse will blow. This is a very reliable
> overvoltage protection, however, at the expense of having
> to replace the fuse.

Yes, this fuse was the one that blew first time, and now shines a bit when 
applying power (i stopped at 7.5v).


<snip>

> In theory IC8, the linear regulator, offers up to 1.5A current.
> The bad thing with linear regulators is, that they keep
> drawing the same amount of current, no matter how high
> the input voltage may be. At 15V input at J2, the regulator
> will still see 12.4V, making an input/output difference
> of 12.4V - 5V = 7.4V. Ethernut 2 may draw about 250-300 mA,
> which means, that the regulator has to destroy
> 7.4V * 0.3A = 2.22W. This power is converted to heat and
> believe me, this is a lot. Not for heating up rooms, but
> for heating up enclosures or burning your fingers.
>
> The final result: 7.6V is the minimum, 9V is just perfect,
> voltages above 12V should be avoided and anything above
> 15V will blow the fuse.

So it should be safe to try it again, at the possiblity the fuse will stop 
working? Because i had the powersupply checked, and it generates indeed 
9v (when set at).


> Btw. newbies typically make the mistake to place the board
> on the conductive shipping bag. This is a bad idea. Putting
> the board on an electrostatic surface is even worse. Never
> ever do it like Adam:
> http://www.sics.se/~adam/img/contiki-ethernut-server.jpg
> Adam is of course no newbie, but many pros simply ignore
> the danger caused by electrostatic discharge.
> Best use a sheet of paper, raw wooden surfaces are perfect
> too. Or mount some legs, so the board will not touch any
> surface.

I had/have it on a stack of paper. So that shouldn't be a problem.


> Beside all that, you board might got broken after it passed
> the final test before shipping. egnite will replace it free
> of charge.
>

This could be a possibility.


Thanks for the long, and detailed reply.


 	 Bas Nedermeijer