Hey everyone, I am developing a power electronics to control the speed of a DC motor using PLC.

I am using the voltage regulator LM350AT along with 4 potentiometers connected to a transistor each, since I need to have 4 different speed channels to switch between.

My problem is I need to have a solution for when none of the potentiometers is activated, I don't want voltage or current to flow. If all of them were off the motor will then be running at full speed depending on the voltage supplied by the power supply.

My circuit diagram is also attached below

Thanks in advance.

Mo

 

Hi mohamhad,
Welcome to AAC.
What are the 4 preset voltage levels.?
E

 

Hey @ericgibbs thanks for your concern.


They are as follows:
4.5V
7V
10V
15V

T

 

Hi,
Have you considered a basic clamp of say 16V zener on the Adj pin of the regulator to 0V.
Or using a 4 Input gate, connected to the MOSFET Gates, which sensed a 0V input to all the Gates and its output pulled the Adj pin low.
E

 

Hi,
Have you considered a basic clamp of say 16V zener on the Adj pin of the regulator to 0V.
Or using a 4 Input gate, connected to the MOSFET Gates, which sensed a 0V input to all the Gates and its output pulled the Adj pin low.
E

I don't understand the principle of the 16 V zener diode, I have looked its datasheet up but couldn't quite get it. However, I find the 4 input gate solution quiet handy.

Thank you for the recommendations, much appreciated.

 

I am guessing that running the motor at full speed is an unacceptable condition at all times. As that is the case, the situation can exist that if the PLC is not active the motor will not be controlled and the speed will increase. So the solution is one more output to switch on the motor poser when it is required, and to switch it off at all other times. That will be the best choice.

The four input NOR gate suggested in post #4, with an adequate buffer transistor, to pull the program input low, may also be applicable. That gate function can also be provided by four signal diodes.