Powering a circuit from BS2 Pin - Transistor Help -

Steel

I know this type of question has been on here several times before in different applications (powering something from a BS2 pin) but I can't seem to find it.

I have a circuit with a few IC's on it that I want to have NO POWER on it, until controlled by a BS2 pin.

When the pin goes HIGH, I want the VCC in the BS2 Circuit to then flow to the NEW_VCC (or VCC in the circuit that currently has no power.)

I attached the schematic of the resistor/transistor setup. I don't feel confident in it, and would just like some feedback.· Should·I use a different transistor?· Should I organize it differently?

Or is there a resource that I can·just get a link to?

Any help would be great.

Again, I need the·NEW_VCC to be available on a HIGH from the BS2 Pin.

Thanks!!

Jason-WI

What you have there wont work. The 2N2222 is NPN and the emitter needs to be the lower potential- your transistor is in backwards.

If you want to use the 2N2222 connect the collector directly to VCC and your load directly to the emitter. No resistor required on the collector. Then use a 470 to 1K ohm on the base to your stamp pin. When the stamp pin goes high the transistor will conduct and power your circuit.

Jason

I forgot to add that you will loose .7V across the transistor. A mosfet would be a better solution if you need the full 5V.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
He who dies with the most toys wins!

Post Edited (Jason-WI) : 6/28/2006 2:58:38 PM GMT

Ryan Clarke

I don't quite understand what you are going for- a quick google on PNP vs NPN should help you better understand which you should use.

Ryan

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Ryan Clarke
Parallax Tech Support

RClarke@Parallax.com

Beau Schwabe

The way your circuit is right now, the 2n2222 is backwards and acting like a diode across the B-E junction.
In order to control the HIGH side or VCC you will need a PNP transistor rather than a NPN.· ...and that's only if VCC is 5V.
If VCC is something other than 5V, you will need 2 transistors (one NPN and one PNP)

In the image on the left, if the Stamp pin is LOW, then "NEW_VCC" will be enabled.· The image on the right,
if the Stamp pin is HIGH, then "NEW_VCC" will be enabled.


▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 6/28/2006 3:13:50 PM GMT