Question about how to amplify power.

[Jack.Straw]

Hello. I'm wanting to drive a solenoid valve with a Picaxe microprocessor. The processor runs on a 5v circuit and my valve requires 12v. The Picaxe documentation says I need to use a MOSFET circuit:

**broken link removed**

The chip i'm using (18M2) runs on 5v and can source 20mA per output pin, with a maximum of 90mA total. My solenoid valve runs on 12v and requires .5 watts. So that is something like 42mA? Do I need to combine the output of several pins, or is there a way to amplify the output of 1 pin?

Thanks for your time,
-Scott

 

[Dr_Doggy]

the transistor(mosfet) is the amp it takes a low current in the base, and with the "gain" factors it to "collector current"(solenoid input pin)

R1 varies with gain value for transistor

 

[Reloadron]

Using the circuit you have pictured you could use a 2N2222 NPN transistor (very common) and about a 120 Ohm base resistor. You could also use as pictured the IRL 520 MOSFET. The MOSFET in the image is a logic level MOSFET designed to work off the 5 volts output of the PIC. Either way leave the 1N4001 in the circuit. That is there to snub the inductive kick when the solenoid coil field colapses at turn off.

Ron

 

[Jack.Straw]

Thanks!!

So this is correct?
**broken link removed**

 

[Reloadron]

That would work fine.

Ron

 

[Jack.Straw]

Thanks for your help Ron, i really appreciate it!

 

[imix500]

You mentioned the valve needs 12v correct? Then you would need a separate 12v supply. Instead of +5 shown in the schematic, you would supply +12v.

 

[Jack.Straw]

imix, yes, the valve is 12v. So i would supply the chip with a 5v power supply, and the solenoid with a separate 12v supply? How would the chip control weather or not the 12 volts reaches the solenoid?

This is what I have so far... how would i work in the 12v?
**broken link removed**

 

[Reloadron]

imix500, good catch that I missed. If you drive your transistor with the 5 volt logic from the PICAXE that will be fine. However make sure the 5 volts and 12 volts share the same common. Also, my bad as figure about a 2.2 K Ohm resistor for the base of the 2N2222. I missed that, sorry as my bad.

Ron

 

[imix500]

Just as you had drawn it. The transistor would switch the 12v with the 5v output. Tie the grounds together and you should be good.

 

[Reloadron]

You want it like the attached.

 

[Jack.Straw]

Awesome, thanks guys!! Does this look correct?

 

[Reloadron]

Yep. That will work.

Ron

 

[imix500]

Just a minor thing, but you have the leads to the solenoid reversed. Also, I would connect the 5v gnd close to the micro and join the touch sensor and 12v gnd there to make a "star ground".

 

[Jack.Straw]

Like this?

 

[imix500]

Looks great.

 

[Jack.Straw]

Awesome, thanks again for all your help!

 

[shortbus=]

Jack.Straw - what program did you use for your bread board schematic? Where did you download it? Thank you.

 

[MikeMl]

Where are your bypass caps for the PIC?

 

[Jack.Straw]

Shorbus, I use DIY Layout Creator. It's a free program:
Download DIY Layout Creator 1.23 Free - A useful tool that will help you easily create board layouts for various components - Softpedia

Mike, this is my first Picaxe project... what do you mean?

Thanks!
-Scott