Installation - 3
39

OVP Considerations

CAUTION: Disabling the OVP protection circuit may cause excessive output voltages, such as can
occur if the remote sense leads are shorted, to damage the equipment under test.
The dc source is shipped from the factory with its overvoltage protection circuit enabled. You can disable
the OVP circuit using either the front panel VOLT PROT command located in the OV menu, or the
VOLTage:PROTection:STATe SCPI command as explained in chapter 8.
The OVP circuit contains a crowbar SCR, which effectively shorts the output of the dc source whenever
the OVP trips. However, if an external current source such as a battery is connected across the output and
the OVP is inadvertently triggered, the SCR will continuously sink a large current from the battery,
possibly damaging the dc source.
To avoid this, either disable the OVP circuit or program it to its maximum value to prevent it from
inadvertently tripping. Additionally, you can connect an external protection diode in series with the
output of the dc source. Connect the anode of the diode to the + output terminal.
The OVP circuit’s SCR crowbar has also been designed to discharge capacitances up to a specific limit,
which is 50,000 µF. If your load capacitance approaches this limit, it is recommended that you do not
intentionally trip the OVP and discharge the capacitance through the SCR as part of your normal testing
procedure, as this may lead to long-term failure of some components.
DVM Connections
CAUTION: The DVM may be damaged if voltages at the input terminals exceed ±50 Vdc to ground.
The DVM connector has three pins: plus, minus, and earth ground. The 3-pin connector is removable and
accepts wires sizes from AWG 22 to AWG 14. Disconnect the mating plug by pulling it straight back.
The DVM is designed as an auxiliary measurement input that can measure voltages on circuits that are
powered by the main output (output 1). Voltage measurements can be made on test points inside the
phone under test, or on test points located on the test fixture that is connected to the main output. Figure
3-7 illustrates a common measurement application for the DVM. This example is only provided for
illustration; your specific application will vary depending on the type of test and type of phone.
Agilent 66309D
A
g
ilent 66311D
OUTPUT 1
+
−
DVM INPUT
lead resistance
lead resistance
Test Fixture
load
current
Minus
terminal
LOAD
+
_
batter
y
connector
connector for
internal phone
circuits
V common mode
-4Vdc < (V comon mode) < +25Vdc
Figure 3-7. DVM Measurement Example