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Power supply for a small hub (L4OT0008CAT)

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john1

Active Member
Hi,

I'm intending to run a small Hub that i have been given.
But i wasn't given the power supply for it.
So i opened it up to see if i could tell what supply to give it.
It has a diode bridge on the input socket, so i assume it wants AC.
This feeds a 'LM2575T-5' small regulator pack, TO-220 package.

I found some info on a 'LM2575T-5.0' which i guess would be the one.
It seems to have an input capability from 7 volts to 40 volts with
a regulated output of 5 volts. (up to one amp)
With an input variation like that i should find a transformer easily.

So i'm guessing that an AC input of around 12 volts would be ok ... ?

Any comments or advice ?

Cheers, John :)
 
If it's got a bridge rectifier you can put DC through it as well.

The maximum input voltage will be limited by the heatsink on the regulator (and the current through it), the higher the voltage the hotter it will get.

If you have a 12V PSU handy (either AC or DC) try it, and see how hot the regulator gets.
 
Hi Nigel,

Yes, you're quite right, i could try it on DC.
I do have a small variable DC supply.
Thats a good idea, i will try it later.

The 'LM2575T-5' seems to be one of the new breed of regulators called
buck-effect or something like that, they dont just monitor the through
current, they pulse the current draw from their supply via a small coil
which inductively sustains power between pulses, and in this way the
current output available is greater than the current draw from its supply.
They claim efficiencies around eighty per cent.

By trying this on a variable DC supply, i may be able to see this 'buck-
effect', i will try moving the voltage supply up and down, and i hope to
see the current draw actually reduce with a rise in voltage.

These units are still quite new to me, this will be my first experience
with one of these new regulators. They still seem a weird arrangement
to my mind, i guess that efficiency (wasted heat) is becoming more
important as size reduces and increasing circuit complexity matters less
than effective cooling.

Thanks for your comments, i feel a little more confident with it now,

Cheers, John :)
 
Well i have finally got around to checking out this little hub
using a small variable DC supply, with amp and volt meter on board.

With no other connections than the supply i expected to raise the
applied voltage to a little over five volts and see what current it
used. Then i expected to raise the applied voltage further without
much effect on the current used.

Maybe even a slight reduction in current drawn, as this is a 'high-
efficiency' type of stabiliser in the unit.

Alas no, the current draw rises with the applied voltage,
the green leds on the front don't get brighter though, so maybe the
stabiliser is delivering a regulated voltage to the internal circuitry.

I did not push it past about 600 mA which it reached at about seven
volts, i tried the DC in both directions with identical results so
it looks like the diode bridge is in good working order.

So now i am possibly going to try it on a variac, with meters attached
or if i find a suitable transformer maybe i will just use it as is.

I dont think i could safely apply up to seventy volts, as described
in the data info on the 'LM2575T-5.0' regulator chip.

I am a bit disappointed, as i had hoped to see the current draw
reduce a little with an increase in applied voltage.
Such is life.

I still don't really have much idea how to use a router, so i will
have to find out as i go.

What does 'COL' mean ?
next to the power on led marked 'PWR', theres a little led marked
'COL' i have no idea what that means.

Theres also a little slide switch with two positions marked '8x' and
'8=' i have no idea what that means either.

Any help much welcomed !

Regards, John :)
 
I wouldn't go much over 12v on the input..The regulator may handle more but the filter capacitors may only be rated for much less..
The 'col' is probably for collision, indicating traffic on the router....
 
Thank you gerty,

I had not intended exceeding about 6.5 to 7 volts,
and i would monitor the current before finalising.

I have looked at the caps on the circuit board inside,
but it is very difficult to figure out what the rated
voltages are, i have not done so yet.

It makes sense that something would indicate traffic.
There are also eight small yellow leds set to one side,
numbered one to eight.

I am hoping that once i get to try and use this hub,
it will make a lot more sense.

Regards, John :)
 
Good point, John1. The input voltage of buck regulator max. 40V, so the input voltage maximum (under 40V) the capacitor voltage. The lower input voltage = higher input current and smaller efficiency. The switchmode regulator like the higher input voltage.
 
Usually the input voltage is labeled on the device, kinda surprised that it isnt.

Can you get ahold of the company that makes it be sure of what the supply is?
 
Hi Nigel, Gerty, Sebi, jrz126,

Yes, usually the supply is labelled up, but on this little hub its not.
The only reason i know its an AC feed is cos i've had it apart, and its
fed straight to a diode bridge.

Anyway, i tried it again, and cos i know roughly the voltage its ok at
from before, i already had it set to seven volts when i switched on the
supply, which looked a bit lower current draw than before although the
lights all looked normal.

So i varied the supply a bit up and down. I was most surprised and
pleased to see that the current draw was less as the voltage went up,
and more as the voltage went down.

This was the behaviour i had expected to see before, but i had been too
cautious before, as i found now, that if the voltage is wound up from
nothing the circuit just takes more current with rising voltage, but
if you switch on an applied voltage between seven and twelve volts
the circuit works as i think it should.

I found the maximum current draw to be @ 95mA at @ 8v falling to @ 50mA
at @ 12v, i did not push it higher than 12v cos i dunno the cap ratings
but it looked like it may have used a little less current if i had.

So i have now seen this peculiar 'buck-effect' for myself.

I am now poking around amongst my collection of small transformers to
find one that i think will be suitable for this little hub.

I am guessing that a small 6.3v transformer would give a suitable voltage
after smoothing, about 8.5v roughly ... ?

Still looking.
Regards, John :)
 
Probably work, but You can use two diodes and two caps as voltage doubler for better efficiency of buck regulator.
 
I had considered making up a doubler on a transformer i looked at
before, i am now using a 'Mains-plug-and-transformer' lump that is
giving me about 14VDC, it seems to be ok.

I have no experience of using a hub, i am going to just plug the
ethrnet cables in and hope for the best.

Any advice would be welcome,

John :)
 
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