Constant Current - Xantrex XPH 75-2D Operating Manual

Constant Current

If the load resistance is low enough such that, at the output voltage set, a current greater than the
current limit setting would flow, the power supply will automatically move into constant current
operation. The current output is adjusted by the CURRENT control and the VOLTAGE controls
set the maximum voltage that can be generated.
The CC lamp lights to show constant current mode.
Instantaneous Current Output
The current limit control can be set to limit the continuous output current to levels down to 10mA.
However, in common with all precision bench power supplies, a capacitor is connected across the
output to maintain stability and good transient response. This capacitor charges to the output
voltage and short-circuiting of the output will produce a current pulse as the capacitor discharges
which is independent of the current limit setting.
Mode Selection
The three operating modes are selected by the front panel rotary switch situated between the
terminals.
Caution. Turn both outputs off before changing mode. Possible damage to the circuit being
powered, and to the unit itself, may occur if the mode is switched with either output still on.
Mode A: With the switch in this position the outputs operate independently and are isolated
from one another. The voltage range on each output is 0-75V and the current range 0-2A.
Mode B: With the switch in this position only Output 2 is active; the voltage range is 0-75V and
the current range is 0-4A. The controls of Output 1 are inoperative and the display is blanked.
The terminals of Output 1 are isolated from those of Output 2.
Note that with the output switch of Output 1 in the 'ON' position the Output lamp still lights but
the terminals remain open-circuit.
Note also that the range and scaling of the current limit control doubles when changing from
Mode A to Mode B, i.e. with the control set for a 1.5A limit in Mode A, the limit becomes 3A in
Mode B. To avoid possible damage to the circuit being tested the outputs should be switched off
before the mode is changed and the current limit set to the desired value before the output is
switched on.
Mode C: With the switch in this position only Output 2 is active; the voltage range is 0-150V
and the current range is 0-2A. The controls of Output 1 are inoperative and the display is
blanked. The red terminal of Output 1 is isolated but the black terminal remains connected
internally to the black terminal of Output 2.
Note that when the output switch of Output 1 is in the 'ON' position the Output lamp still lights
but the red terminal remains open-circuit.
Note also that the range and scaling of the voltage controls of Output 2 double when changing
from Mode B to Mode C, i.e. with the controls set for 60V in Mode B the output voltage becomes
120V in Mode C. Care should therefore be taken to ensure that the outputs are switched off
before the mode is changed and that the output is set to the correct voltage before it is switched
on.
Protection
The output has intrinsic short-circuit protection and is protected from reverse voltages by a diode;
the continuous reverse current must not exceed 3 Amps, although transients can be much higher.
The output is protected against externally applied forward voltages of up to 85V (Modes A and B)
or 170V (Mode C).
8