Programming Overvoltage Protection - HP 654 A Series Operating Manual

For an HP 6552A supply, Imax = 25.594 amperes and Vmax = 20.475 volts. If you program
the output for <<25 amperes at 20 volts, the supply will operate in the CV mode for all
resistances >0.8 ohms. This represents the operating resistance shown as = C in Figure
5-2. The supply will vary the output current to maintain a constant voltage of 25 volts. If the
load resistance is <0.8 ohms, the supply will vary its output voltage to maintain a constant
current output of 25 amperes. However, if you reprogram the output voltage to a lower value
Vs (see Figure 5-2), then the supply will again be able to maintain CV operation with the
lesser load resistance, such as Rl=B in Figure 5-2,
Programming Overvoltage Protection
Overvoltage protection guards the load against voltages that reach a specified value above the
programmed output voltage.
Setting the OVP Level
Assuming that a power supply is programmed for 10 volts, you can set the OVP level to 11.5
volts as follows:
■ Press (^. The display will change from meter mode to indicate OV, followed by the present
OVP value.
■ Press
0CDQ(DCE3
■ The display will return to the meter mode and indicate the output (10.000 volts)
■ Press
again. The display will now indicate OV 11.500
■ Press (
Enter
1 to return to the meter mode
Checking OVP Operation
Assuming the above operating conditions, trip the OVP circuit as follows:
■ Raise the output voltage close to the trip point, such as 11.0.
m
Gradully increase the output voltage by pressing fTvoitagel until the OVP circuit trips. This
will cause:
□ the output voltage to drop to zero and the Prot annunciator to go on.
H There now is no power supply output due to an overvoltage condition.
■ To verify this, press (
protect
]
and observe that the display indicates OV.
Clearing the OVP Condition
the OVP tripped, return to the meter mode and try to clear the condition by pressing
[Prot Clear).
Nothing
Will
appear to happen because the CV trip point is still below the
programmed output voltage. Thus, as soon as the circuit is cleared, it trips again. You can
clear the OV condition by:
M lowering the output voltage below 11.5 (the OV setting),
■ or by raising the OV trip voltage above the output voltage setting.
Try either of these methods. Now when you press (prot Clear), the Prot annunciator will go off
and the output voltage will return to normal.
Note
In Series 654xA and 655xA supplies, the OVP circuit shorts the power supply
output through an SCR. If the load maintains current through the SCR, the
above methods will not clear an OVP trip condition. You must first remove
the external current source before attempting to clear OVP.
5-6 Front Panel Operation
Overvoltage Protection