FET circuitry

[Dave_colq]

Hi,

I have a project where I need to cycle the power on a 2.5” HDD, The
power cycle is controlled by a micro. The drive need to be on during
startup and switched off when the port pin on the micro is high. The
micro does some initialization during startup for 5 secs (erasing
SRAM, loading data) so it can’t just switch the drive ON straight
away. I was thinking of using a micro to a BJT to a FET but am not
sure of the circuitry needed, again it needs to be on straight away
and then switches off when the micro pin goes high, any idea guys?

Any help would be greatly appreciated.

Dave

 

[John Fields]

On Mon, 2 Feb 2009 02:45:12 -0800 (PST), Dave_colq
<David.Colq@googlemail.com> wrote:

Hi,

I have a project where I need to cycle the power on a 2.5” HDD, The
power cycle is controlled by a micro. The drive need to be on during
startup and switched off when the port pin on the micro is high. The
micro does some initialization during startup for 5 secs (erasing
SRAM, loading data) so it can’t just switch the drive ON straight
away. I was thinking of using a micro to a BJT to a FET but am not
sure of the circuitry needed, again it needs to be on straight away
and then switches off when the micro pin goes high, any idea guys?

Any help would be greatly appreciated.

---
Assuming the port is an output, is active, and is low during power-up:
(View in Courier)


+V>-------------------+
|
S
ľC PIN>-------------G PCH
D
|
[HDD]
|
GND>------------------+

JF

 

[DJ Delorie]

Since most MCU ports are hi-Z on powerup, a pull-down resistor might
be needed too.

 

[John Fields]

On 02 Feb 2009 10:41:13 -0500, DJ Delorie <dj@delorie.com> wrote:

Since most MCU ports are hi-Z on powerup, a pull-down resistor might
be needed too.

---
Sure wouldn't hurt!

JF