Push / Pull Driver ?

i want to be able to send +15 and -5v to control a switching device

i want to use an arduino PWM output to do the switching

two questions

  1. will this circuit work ?

  2. what is the easiest way to take a positive voltage - ie 15V and convert it to -5v

any comments appreciated

"easiest way"

Kinda depends on how much current you need. What is your -5V current requirement?

Might be easier to use an isolated 20V source, use its ground as -5v, and create 5V from the 20V to use as the ground.

Hi Crossroads,

thanks for your commnets

the current requirements are quite small, it is to switch a gate

i have a laptop 20V DC power adaptor i could use for this project

how do i get the +15V and -5V from it ?

A potential divider?

You could use an op-amp comparator using +15 and -5 on it's power rails. Bias -input to +2.5vdc and wire + input to arduino output pin. This is assuming the op-amp can sink and source the current requirements for your load, which you haven't stated.

Lefty

Crazy idea (please validate before destroying something): A 7805? You will get 5V that would be used as Common. Then, between 20V and common you get 15v, and between common and "the other pole from the supply, formerly known as ground" you'll get -5V (play with your multimeter and place the black probe on common).

which one is the crazy idea ? a push pull with negative volts, the voltage divider or the op amp ?

It is possible to produce a negative voltage with a voltage divider ?

No, it isn't.
(Third question, but it's all relative)

two questions

  1. will this circuit work ?

No.
You need a PNP transistor.

hmmm

i thought the transistor on the right was pnp

It's upside down to normal, but it looks like an NPN too me

whoops - original picture modified :roll_eyes:

So now how will you turn it off? The base needs to be at -5V to turn it off and you can only change that signal between zero and +5.
Hint you need another transistor.

Mike, how does it look now ?

More wrong than before.
Want me to tell you yet? I was wrong about the extra transistor you can do it in two.

please tell me more

i found this which is very similar to my design

http://www.ecircuitcenter.com/circuits/pushpull/pushpull.htm

Do you want a "real" push pull or just a signal that goes from +15 to -5?

Attached is an example of the latter. For a real push pull you need another two transistors. Feed the output of this circuit through a resistor to the push pull pair that you posted.

Up_Down.pdf (12.8 KB)

Hi Mike,

thanks for the diagram, it looks pretty good

can the -5 volts interfere with the value of the +15v ?

There is a IC that can give you -5v with only 2 capacitors. ICL7660/MAX1044. You will need a 7805 to convert that 15v to 5v for its input. It can only handle 100mA.
pdfserv.maxim-ic.com/en/ds/ICL7660-MAX1044.pdf