Circuit question

[John Fields]

On Mon, 13 Jun 2011 22:44:23 +0800, Man-wai Chang
<toylet.toylet@gmail.com> wrote:

If you are lucky and you use standard 3A silicon diodes, it *MAY* get
the output voltage in spec for USB. You probably need a small minimum
load to keep the voltage down and prevent it from damaging the hub when
no devices are connected - a 100 ohm 1/2W resistor across the output
after the diodes would be a good idea.

I won't connect more than 2 USB devices to the usb. SO I am NOT trying
to overdraw from the AC adaptor.

---
You haven't yet stated how much current your supply can deliver or, if
in fact, if it's even regulated.

Wanna try to jump that hurdle now?

--
JF

 

[Jamie]

Rich Grise wrote:

Man-wai Chang wrote:


You can put two diodes in series, it will drop 2 x 0.6 volt.

What diode? Name?


1N4148, 1N914, etc. - any general-purpose silicon diode.

Have Fun!
Rich

Hmm, I really don't think a 914 is going hold under the stress!

Jamie

 

[krw@att.bizzzzzzzzzzzz]

On Mon, 13 Jun 2011 22:43:35 +0800, Man-wai Chang <toylet.toylet@gmail.com>
wrote:

1N4148, 1N914, etc. - any general-purpose silicon diode.

Quite expensive a piece. Thanks.

$.38 is quite expensive? What do you consider cheap? BTW, they're about a
penny in bulk.

 

[Michael A. Terrell]

Man-wai Chang wrote:

1N4148, 1N914, etc. - any general-purpose silicon diode.

Quite expensive a piece. Thanks.

Those are signal diodes, not power diodes. As usual, Rich is full of
it.


--
It's easy to think outside the box, when you have a cutting torch.

 

[Rich Grise]

Michael A. Terrell wrote:

Man-wai Chang wrote:

1N4148, 1N914, etc. - any general-purpose silicon diode.

Quite expensive a piece. Thanks.

Those are signal diodes, not power diodes. As usual, Rich is full of
it.

Signal diodes also drop .6v, and Man-wai never has said how much current

needs to go through the diodes.

So, what's with this personal hardon for me? You never miss a chance to
throw a limp barb at me - have you got a man-crush that you're ashamed of?

Thanks,
Rich

 

[Man-wai Chang]

You haven't yet stated how much current your supply can deliver or, if
in fact, if it's even regulated.

It is a Nokia ACP-9X. Label said:

Input: AC 100-220V, 160mA, 50-60Hz
Output: DC 6.2V, 720mA.

I think it's already regulated.

Wanna try to jump that hurdle now?

Um... what hurdle? If you were talking about overdrawing more than
720mA, NO NO NO!


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[Man-wai Chang]

unless they both draw the maximum 500mA you could use 1N400x series 1A
diodes. If you use too weak a diode it will probably fail short-circuit
and blow up the hub and all connected USB devices and maybe your USB port.

The USB hub has been modified to charge iPod and MP3 player.

.. fused at 3A or over - e.g. a scrap PC power supply. If you find the
bridge rectifier is a single component, short its positive and negative
output terminals and you will have a two diode drop if you put it in
series via its input terminals with your 6.2V PSU and load. DON'T FORGET
the 100 ohm half watt load resistor I mentioned, and CHECK the maximum
output is less than 5.25V BEFORE you connect it to the hub.

I know how to read a resistor's value, but not a diode.

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[Man-wai Chang]

Those are signal diodes, not power diodes. As usual, Rich is full of
it.

Come on, focus focus! Focus on the circuit!

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[IanM]

Man-wai Chang wrote:

unless they both draw the maximum 500mA you could use 1N400x series 1A
diodes. If you use too weak a diode it will probably fail short-circuit
and blow up the hub and all connected USB devices and maybe your USB
port.

The USB hub has been modified to charge iPod and MP3 player.

NOW you tell us . . . .
It is likely that both are designed to take 500mA when charging,
possibly even more if they think you have connected their dedicated
charging adapters.

We now know the PSU is under 1A so its not fit for purpose.
===========================================================

If you want to build a single device charging station with it, you
could, but in that case you wouldn't need a hub . . .

.. fused at 3A or over - e.g. a scrap PC power supply. If you find the
bridge rectifier is a single component, short its positive and negative
output terminals and you will have a two diode drop if you put it in
series via its input terminals with your 6.2V PSU and load. DON'T FORGET
the 100 ohm half watt load resistor I mentioned, and CHECK the maximum
output is less than 5.25V BEFORE you connect it to the hub.

I know how to read a resistor's value, but not a diode.
Power diodes have a type number printed on them. It may not be the full

number so one needs some experience to guess if it should for instance
have 1N added in front, but you can usually identify them.

If not, find a different used diode, or guess their characteristics from
the ratings of associated components in the circuit they were in.

Some signal diodes use coloured bands for their code, some use a printed
number and some are just unidentifiable, but signal diodes are rarely
worth salvaging.

If you hunt for diodes in the part of the circuit I suggested, and the
fuse is over 3A they *WILL* have an adequate rating for this project.


--
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[Man-wai Chang]

It is likely that both are designed to take 500mA when charging,
possibly even more if they think you have connected their dedicated
charging adapters.
We now know the PSU is under 1A so its not fit for purpose.

Ok. Then I plug in just one.

If you want to build a single device charging station with it, you
could, but in that case you wouldn't need a hub . . .

The hub has 4 USB ports, plus an input. It's still money!

Power diodes have a type number printed on them. It may not be the full
number so one needs some experience to guess if it should for instance
have 1N added in front, but you can usually identify them.

If not, find a different used diode, or guess their characteristics from
the ratings of associated components in the circuit they were in.

Some signal diodes use coloured bands for their code, some use a printed
number and some are just unidentifiable, but signal diodes are rarely
worth salvaging.

If you hunt for diodes in the part of the circuit I suggested, and the
fuse is over 3A they *WILL* have an adequate rating for this project.

Thanks. Let me find out whether a new one is cheap.

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[Jasen Betts]

On 2011-06-12, Man-wai Chang <toylet.toylet@gmail.com> wrote:

I found a un-used 6.2V AC adaptor, and would like use it to power a USB hub.

We all knew that USB takes 5V as input.

I am going to use a 10k and a 40K resistor to make a potential divider
to reduce 6.2V to about 5V.

Is the wiring diagram correct?

it depends on the plug, (different sockets hare the pins arranged
differently) but usually the inner conductor is positive
and the outer is ground,

Would the input current be affected?

yes. resistive dividers only work when you need no current at all.
the more current you need the more of an approximation they become.
the higeger the resistance used the worse it gets.

For this reason they are unsuited for reducing power supply voltage
except in a few special cases - like the timers in pop-up toasters.

--
⚂⚃ 100% natural

 

[Man-wai Chang]

yes. resistive dividers only work when you need no current at all.
the more current you need the more of an approximation they become.
the higeger the resistance used the worse it gets.

For this reason they are unsuited for reducing power supply voltage
except in a few special cases - like the timers in pop-up toasters.

So I should use diode or regulators? Thanks.

--
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[krw@att.bizzzzzzzzzzzz]

On Tue, 14 Jun 2011 20:14:20 +0800, Man-wai Chang <toylet.toylet@gmail.com>
wrote:

yes. resistive dividers only work when you need no current at all.
the more current you need the more of an approximation they become.
the higeger the resistance used the worse it gets.

For this reason they are unsuited for reducing power supply voltage
except in a few special cases - like the timers in pop-up toasters.

So I should use diode or regulators? Thanks.

How about buying the right wall wart?

 

[Man-wai Chang]

How about buying the right wall wart?

Don't wanna waste that Nokia AC adaptor!!! Could I?

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[krw@att.bizzzzzzzzzzzz]

On Wed, 15 Jun 2011 00:25:00 +0800, Man-wai Chang <toylet.toylet@gmail.com>
wrote:

How about buying the right wall wart?

Don't wanna waste that Nokia AC adaptor!!! Could I?

Use it as a fishing weight. That's it's best use.

 

[ehsjr]

Man-wai Chang wrote:

yes. resistive dividers only work when you need no current at all.
the more current you need the more of an approximation they become.
the higeger the resistance used the worse it gets.

For this reason they are unsuited for reducing power supply voltage
except in a few special cases - like the timers in pop-up toasters.


So I should use diode or regulators? Thanks.

You need to answer the question you were asked earlier.
Is this a regulated supply. You cannot guess, you must
*know*. If it is regulated, then two 1N400X diodes, as
was mentioned in a reply, will work for you. If it is
not regulated, you must regulate it.

If you cannot, or will not, determine if the thing is a regulated
supply, then just buy something suited to the task.

Ed

 

[Man-wai Chang]

You need to answer the question you were asked earlier.
Is this a regulated supply. You cannot guess, you must
*know*. If it is regulated, then two 1N400X diodes, as
was mentioned in a reply, will work for you. If it is
not regulated, you must regulate it.

Could I use a multimeter to find out?

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[John Fields]

On Wed, 15 Jun 2011 15:00:51 +0800, Man-wai Chang
<toylet.toylet@gmail.com> wrote:

You need to answer the question you were asked earlier.
Is this a regulated supply. You cannot guess, you must
*know*. If it is regulated, then two 1N400X diodes, as
was mentioned in a reply, will work for you. If it is
not regulated, you must regulate it.

Could I use a multimeter to find out?

---
Do you know how to use a multimeter?

--
JF

 

[tuinkabouter]

Op 6/13/2011 12:59 PM, Man-wai Chang schreef:

You can put two diodes in series, it will drop 2 x 0.6 volt.

What diode? Name?

Your adapter can deliver max 720 mA. So a 1A rated diode is sufficient.
Google for: Diode 1A
You find Fairchild 1N1007 cost $ 0.0265 when delivered on a production
roll. In an electronic part shop it is a bit more.
But any 1A or more rated diode is ok.

--
pim.

 

[Man-wai Chang]

Is this a regulated supply. You cannot guess, you must

Could I use a multimeter to find out?

Do you know how to use a multimeter?

Tell me what to do!!!

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