Voltage mode and current mode.
Most Spellman high voltage power supplies offer an automatic crossover between voltage and current modes, depending on the settings and load conditions. This requires the power supply to have two regulation loops: voltage mode and current mode. In addition, each loop requires a user-supplied programming signal so that the power supply can be adjusted and limited accordingly.
Voltage Mode
Most customers use our power supplies operating in voltage mode. When the power supply is operating in voltage mode, it behaves as a voltage source. Depending on the setting selected, the power supply will actively regulate from 0 to 100% of the rated output voltage.
The output current in this case is determined by the magnitude of the output voltage and the impedance of the load on the power supply. Most users set the current mode to the maximum value. In this case, if a short circuit occurs at the power supply’s output, it will automatically switch from voltage mode to current mode, regulating the current to 100% of the maximum rated current.
Current Mode
Our customers rarely run their power supplies in current mode. When the power supply is operating in current mode, it behaves as a current source. Depending on the setting selected, the power supply will actively regulate from 0 to 100% of the rated output current.
In this case, the output voltage is determined by the amount of output current and the load’s impedance on the power supply. Most users set the voltage mode to the maximum value. In this case, if a loop is opened on the power supply, it will automatically switch from current mode to voltage mode, adjusting the voltage to 100% of the maximum rated voltage.
Voltage mode/current mode programmability
Both the voltage and current loops are set to 100% of the rated output in the above case. These signals are still usually programmable, ranging from 0 to 100%, depending on the needs of the customer application.
Mode Single Selectivity
As mentioned above, a typical high voltage power supply can only adjust one parameter (voltage or current) at a time. If you are running voltage mode, then you have adjusted the compatible voltage and current. If you are running current mode, you are already adjusting for both current and voltage. The point to emphasize here is that the power supply cannot be adjusted for both voltage and current. If operating in voltage mode (as most people do), the power supply will regulate the output voltage. Still, the current drawn from the power supply will depend on the voltage setting and the impedance of the loaded power supply.
