Power from USB & DC Adapter (was Re: Design Files/Gerbers of SAKC V2)

Ron K. Jeffries rjeffries at gmail.com
Fri Jul 30 10:56:49 EDT 2010


Please make sure that the design protects
against plus and minus being plugged in wrong.
I think that implies a zener diode.

the extra cost of a 5V supply that accepts a fairly
wide range of input voltage say 12v or less
is probably worth it IMO

SAKC is prolly less price sensitive than Nanonote.

---
Ron K. Jeffries
http://ronkjeffries.posterous.com








On Fri, Jul 30, 2010 at 07:44, Carlos Camargo <cicamargoba at gmail.com> wrote:

> Hi Adam
>
>
>
>
> On Fri, Jul 30, 2010 at 8:53 AM, Adam Wang <adam at sharism.cc> wrote:
>
>> Hi,
>>
>> 1, I made a mistake on D10 footprint confirmation, It must be 0805 to meet
>> MSCD104H. Pls change this to 0805 package.
>>
>
> ok, I'll fix it
>
>
>
>
>> 2, maybe mark a concentric circles with central ring to mark "+" and outer
>> ring marked a "-" nearby DC Jack to suffer from mistakes by novices.
>>
>
> Agree
>
>
>
>>  3, last but not least, current design of SAKC V2 have a condition that
>> is it can not use +5V power at the same time either from USB cable (0.5A) or
>> DC adapter(can be more). If using DC adapter fixed +5V in already,
>> you must _remember_ to take out mini-jumper on J18 first, then plug-in usb
>> cable to do s/w work. If you forgot that take out mini-jumper, after
>> plugging usb cable; There must be have power +5V "collide" together. This
>> UNSAFE condition will be happened once mindless to forget to take out
>> mini-jumper. And possibly let USB host device to be have damage or even DC
>> adapter source. Also if remove DC adapter, the SAKC it can only get 0.5A
>> from usb, unworthy a bit. so
>>
>
>
>> 1) remove the DC adapter reducing the hardware hacking usability of the
>> board a lot.
>>
>
>
>> 2) remove USB power, adding the need for an extra power adapter for every
>> user.
>>
>
>
>> 3) add additional circuitry to make both USB & DC power stable in all
>> cases. User should have the chance to update s/w from USB while still some
>> h/w parts connected to SAKC board's extendable 40pins header to get 3.3V
>> supply( actually comes from 5V) to outside application.
>>
>
> Yes, I'm trying to solve this issue, I think that we can use a single
> circuit Power On Reset + Transistor:
>
>                             TRANSISTOR
> USB_VCC-------------|S|           |D|----------- 5V
>                                                        |
>                                      |G|              |
>                                        |               |
> DC_WALL------|  POR |----------------------
>
>
>
> When DC_WALL = 0V  Transistor is ON so 5V = USB_VCC
> when DC_WALL >= POR's threshold => Transistor is OFF =>  5V = DC_WALL
>
>
>
>> Also if SAKC comes with capability of having strong wide power range
>> input, this can make/let additional circuities connected to SAKC easiler and
>> more flexible with ONLY one DC adapter. Fg. real ROBOT industries works
>> around +12V or +9V supply. IMO if this can be true. SAKC will be more
>> stronger. Surely aside from cost evaluation.
>>
>
> We can't provide all the possible voltages for all the possible
> applications. We can add an additional 5v regulator with a wide input range,
> but this increase the cost & the size.
>
> Carlos
>
>
>
> --
> Carlos Iván Camargo Bareño
> Profesor Asistente
> Departamento de Ingeniería Eléctrica y Electrónica
> Universidad Nacional de Colombia
> cicamargoba at unal.edu.co
>
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