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

Carlos Camargo cicamargoba at gmail.com
Fri Jul 30 10:44:20 EDT 2010

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.


>  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:

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 Iván Camargo Bareño
Profesor Asistente
Departamento de Ingeniería Eléctrica y Electrónica
Universidad Nacional de Colombia
cicamargoba at unal.edu.co
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