#2 L708CV Circuit

I simply want to connect 2 motors as i show in the image, using a 12VDC power source and 2 #L7809CV, right now the circuit is this you can see in the image i made. The GND its the same source for every wire connected to.

What happens: When motor number 1 absorb power, motor 2 absorb the same power at the same time, and viceversa, if number 2 is on, number 1 power up too.

What i'm looking to do: When motor 1 is absorbing power, motor 2 still off, and viceversa, if number 2 is On then number 1 still off, and the motors have to be powered on both, or turned off both.

Sorry my english, i think this its not hard to do so i post the image that can talk more than my english. I guess :)


Here is an other image:enter image description here

As you can see there are 2 pcb who command the input and output for each motor, those pcbs are powered on by a different 3,3v line but use the same GND of other components.

Its important to let there only one 12v source line for both L7809.


If I am getting it correct you wish to run only one motor at a time.
That can be simply done using only one LM7809 and a SPDT switch.


simulate this circuit – Schematic created using CircuitLab

I guess that is too obvious. So would you like to add more info. Like any specific control mechanism( supposedly to replace the manual SPDT switching).

  • \$\begingroup\$ This can be a good solution, but in an other case. Sorry i forgot this: there will be the opportunities to use the motors at the same time or one by one or all motors off. Without a manual switch, i was thinking to use some diodes... \$\endgroup\$ – checco Dec 23 '14 at 22:53
  • \$\begingroup\$ I can't change the circuit schematic, i have just to fix it for the necessity. \$\endgroup\$ – checco Dec 23 '14 at 23:07
  • \$\begingroup\$ @checco you need to provide additional info regarding the input/cause to make motors run. You can draw a simple table depicting when to run which motor. \$\endgroup\$ – vvy Dec 24 '14 at 4:20

Maybe this is what you are looking for:


simulate this circuit – Schematic created using CircuitLab

Since each motor is switched with a separate MOSFET the current draw for each motor is guaranteed to be taken from the respective regulator. The control signals for the MOSFETs are logically 'or'd.

You can accomplish the same thing with a switch with multiple contacts rather than the diodes and MOSFETs. The switch for "both" motors needs to have individual contacts for each motor.

  • \$\begingroup\$ your answer would be great if i can avoid to use a manual switch. \$\endgroup\$ – checco Dec 24 '14 at 16:27
  • \$\begingroup\$ You have not explained what you do intend to use. The above scheme requires a voltage (9V) for each desired state - doesn't have to come from a switch. \$\endgroup\$ – Spehro Pefhany Dec 24 '14 at 16:46
  • \$\begingroup\$ let me build this and try, i am the noob here and maybe i am not understanding very well how this work. I suspend the theory and going to do the practice. I'll let you know how this goes... \$\endgroup\$ – checco Dec 24 '14 at 23:20

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