simple power switching circuit

[none1]

Hello,

I am working on a small project using a pic microcontroller that
I want to have run for months at a time. I can put the pic to sleep
to conserve power but I would also like to remove power to the
peripherals I am adding (i2c eeprom, etc). What I want to do is
use one of the pic output pins (high) to power up the devices when
I need to use them. This seems like it should be pretty easy, can
anybody point me to a simple circuit to do this or recommend a good
way to do this.

thanks !

 

[Jamie]

none1 wrote:

Hello,

I am working on a small project using a pic microcontroller that
I want to have run for months at a time. I can put the pic to sleep
to conserve power but I would also like to remove power to the
peripherals I am adding (i2c eeprom, etc). What I want to do is
use one of the pic output pins (high) to power up the devices when
I need to use them. This seems like it should be pretty easy, can
anybody point me to a simple circuit to do this or recommend a good
way to do this.

thanks !
Look for a logic Mosfet transistor that can be gate driven via

an output of the PIC.
A high side P-channel config should do it. That would be the
S (Source) to the + rail, G (gate) via a parasitic resistor
to an output of the pic. (D) drain will supply the peripherals.
The pic's output will have to go low to turn on the fet.
Select a fet that has full turn on at 50% or less of the rail
voltage you're using..
That's about the drift of it..
P.S.
Make sure you have the output of the pic programmed for pull up.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[none1]

On Sun, 11 Nov 2007 14:52:45 -0700, Jamie wrote:

none1 wrote:

Hello,

I am working on a small project using a pic microcontroller that
I want to have run for months at a time. I can put the pic to sleep
to conserve power but I would also like to remove power to the
peripherals I am adding (i2c eeprom, etc). What I want to do is
use one of the pic output pins (high) to power up the devices when
I need to use them. This seems like it should be pretty easy, can
anybody point me to a simple circuit to do this or recommend a good
way to do this.

thanks !
Look for a logic Mosfet transistor that can be gate driven via
an output of the PIC.
A high side P-channel config should do it. That would be the
S (Source) to the + rail, G (gate) via a parasitic resistor
to an output of the pic. (D) drain will supply the peripherals.
The pic's output will have to go low to turn on the fet.
Select a fet that has full turn on at 50% or less of the rail
voltage you're using..
That's about the drift of it..
P.S.
Make sure you have the output of the pic programmed for pull up.

Thank you.

Is there a mosfet which will do the same thing you describe except with
the gate being pulled high to turn on ? All the pins on the pic will powerdown I
think when I put it to sleep, plus I would like a circuit that draws no
power when the pic is sleeping. I'm not sure how much power the mosfet
draws when 'turned off' with the pull up resister.

 

[Eeyore]

none1 wrote:

Hello,

I am working on a small project using a pic microcontroller that
I want to have run for months at a time. I can put the pic to sleep
to conserve power but I would also like to remove power to the
peripherals I am adding (i2c eeprom, etc). What I want to do is
use one of the pic output pins (high) to power up the devices when
I need to use them. This seems like it should be pretty easy, can
anybody point me to a simple circuit to do this or recommend a good
way to do this.

Yes, it's very practical. What kind of peripheral (voltage/current) do you need
to power up/down ? That will influence the design.

Graham

 

[Eeyore]

none1 wrote:

Is there a mosfet which will do the same thing you describe except with
the gate being pulled high to turn on ? All the pins on the pic will powerdown I
think when I put it to sleep, plus I would like a circuit that draws no
power when the pic is sleeping. I'm not sure how much power the mosfet
draws when 'turned off' with the pull up resister.

If using a mosfet to switch the load I'd suggest an n-channel type with a high side
driver chip. IR do lots of high side drivers and I think Microchip even has some.

Graham

 

[Nobody]

On Mon, 12 Nov 2007 01:03:22 +0000, Eeyore wrote:

Is there a mosfet which will do the same thing you describe except with
the gate being pulled high to turn on ? All the pins on the pic will powerdown I
think when I put it to sleep, plus I would like a circuit that draws no
power when the pic is sleeping. I'm not sure how much power the mosfet
draws when 'turned off' with the pull up resister.

If using a mosfet to switch the load I'd suggest an n-channel type with a high side
driver chip. IR do lots of high side drivers and I think Microchip even has some.

Out of curiosity, what's the advantage of using an n-channel type?

 

[ian field]

"Nobody" <nobody@nowhere.com> wrote in message
newsan.2007.11.12.12.08.24.810550@nowhere.com...

On Mon, 12 Nov 2007 01:03:22 +0000, Eeyore wrote:

Is there a mosfet which will do the same thing you describe except with
the gate being pulled high to turn on ? All the pins on the pic will
powerdown I
think when I put it to sleep, plus I would like a circuit that draws no
power when the pic is sleeping. I'm not sure how much power the mosfet
draws when 'turned off' with the pull up resister.

If using a mosfet to switch the load I'd suggest an n-channel type with a
high side
driver chip. IR do lots of high side drivers and I think Microchip even
has some.

Out of curiosity, what's the advantage of using an n-channel type?

It helps the manufacturer sell an extra high-side driver chip.