What is the difference between Sinking and Sourcing with 0-10 volt Control Systems?

This is an interesting topic, which is often confused in the lighting industry.  This will be a very brief tutorial on the difference between Sinking and Sourcing with a 0-10 volt control wire system.

We will start with the simpler of the two systems (in my opinion), which is the Sourcing of 0-10 volt control.  In this scenario, 0-10 volt DC (can be other voltages, as well as from typically 5-28vdc) is produced by a “Control Station” which then sends the voltage to a “Light” which is turned brighter or dimmer based upon the amount of voltage applied from the Control Station or Source (hence the name Sourcing).  Typically, 0 volts is off and the higher the voltage, the brighter the “Light” becomes and the lower the voltage the dimmer the Light becomes.

Sourcing was commonly used in analog commercial dimmers in the 1970s and earlier as the control signal.  In fact, almost all current commercial dimmers still use Sourcing for their control of the dimmers, but the output of the 0 to 5 vdc is done at the control module in the dimmer rack/pack.

Okay, that was fun.  Hopefully, that explains Sourcing Systems.

Now, let’s try to explain what Sinking is for 0-10 volt control systems.  In a Sinking System the control voltage is produced by the “Light” and not by the “Control Station” (remember Sourcing is the opposite).  The “Light” produces the voltage, typically 10 volts DC, which is then sent to a “Control Station”, which uses a resistor to ground the voltage.  This grounding of the voltage allows the 10vdc to be either increased (no grounding) or lowered (a lot of grounding), which causes the voltage to go down to as low as 0 volts DC.

If the voltage is 1 volt DC, then the “Light” will go to approximately 10 percent of its level.  If the voltage is at 5 volt DC, then the light will go to approximately 50 percent of its level, and so on.

This means that the “Control Station” in a Sinking System does NOT produce any voltage at all, but instead REGULATES the 0-10 volts, which allows the “Light” to go to the correct level.  All dimming in a Sinking System is really done at the “LIGHT” and not at the control station.

A Sinking System and a Sourcing System are NOT compatible and should not be used together.  If you try to use them together, you will not have a good result and there will be a lack of control.

Today, a lot of LED Drivers and Fluorescent Ballasts are using the 0-10 volt Control System of Sinking (not Sourcing).

Since the LED Driver industry is a quickly evolving industry there are a LOT of manufacturers in the industry currently.  One very important note is that LED Drivers should have “isolated” Class 2 and Class 1 circuitry.  Some of the manufacturers are not isolating class 1 and class 2 circuitry on the LED Driver.  This is VERY dangerous, because high voltage (greater than 24vdc and sometimes up to 277vac) can get on to the 0-10 volt control wires.  As you can imagine, this does very bad things to the 0-10 volt control wires, but more importantly the “Control Stations”, which are trying to regulate the 0-10 volts on a Sinking System.  Make sure that the LED Drivers have isolated Class 1 and Class 2 circuitry.

Hopefully, the information in this blog is helpful.

If you have any questions, please feel free to send me a message and I will do my best to answer your questions.

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