1.1. Output Regulation States
The XR Series MagnaDC power supply can operate in either constant voltage or constant current output regulation. The MagnaDC power supply will automatically switch between the two regulation states as a function of the programmed set points and the load impedance. The regulation state is indicated by an illuminated LED above the respective programming knob, also via the external user I/O connector or by computer command.
The XR Series MagnaDC power supply will make a seamless autocrossover from voltage mode control to current mode control, as determined by the voltage and current set points and/or load impedance. If either set point is set to zero, the other set point control will have little or no effect, forcing either a zero voltage limit or zero current limit and preventing output from the MagnaDC power supply.
1.1.1. Constant Voltage
When the constant voltage regulation state is indicated, the MagnaDC power supply is maintaining fixed voltage at the programmed set point, while the output current fluctuates as a function of the load impedance, as illustrated by Fig. 1.1.
To force the XR Series MagnaDC power supply to constant voltage mode, begin with the product in standby and set both voltage and current set points to zero. While pressing the V/I DIS key on the front panel, advance the voltage and current set points for the desired output voltage and the desired crossover current. The crossover current is the maximum desired current, at which the power supply crosses over to current mode control to become a constant current source.
Connect the load and command the power supply to start. The output voltage should be close to the voltage set point. If a load change causes the programmed current set point to be exceeded, the power supply will automatically crossover to constant current output at the programmed current set point and the output voltage will drop proportionately. When setting the current limit, allowance must be made for high peak currents which can cause unwanted crossover.
1.1.2. Constant Current
When the constant current regulation state is indicated, the MagnaDC power supply is maintaining fixed current at the programmed set point, while the output voltage fluctuates as a function of the load impedance, as illustrated by Fig. 1.2.
To force the XR Series MagnaDC power supply to constant current mode, begin with the product in standby and set both voltage and current set points to zero. While pressing the V/I DIS key on the front panel, advance the voltage and current set points for the desired output current and the desired crossover voltage. The crossover voltage is the maximum desired voltage, at which the power supply crosses over to voltage mode control to become a constant voltage source.
Connect the load and command the power supply to start. The output current should be close to the current set point. If a load change causes the programmed voltage set point to be exceeded, the power supply will automatically crossover to constant voltage output at the programmed voltage set point and the output current will drop proportionately.
1.1.3. Pulse Loading
The XR Series MagnaDC power supply will crossover automatically in response to output current or output voltage exceeding the programmed set point. With the set points programmed at average values, high peak loads — as encountered in pulse loading — may cause unwanted crossover. When pulse loading, the set points should be programmed for the peak requirement, not the average.
There are internal capacitors across the output terminals of the MagnaDC power supply. These capacitors help to supply high-current, short-duration pulses during constant voltage operation. Adding external capacitance across the load improves pulse loading capability further, but reduces the protection provided by the constant current circuit; a high-current pulse may damage load components before the average current rises enough to cause the constant current circuit to respond.