Specifications

5.14.1 External current bias circuit in 4TP configuration
For external current bias measurement using other auto-balancing bridge instruments, an external
DC current source and a protection circuit are required. The following describes a protection circuit
that can be used for DC bias current measurements up to 10 A. Figure 5-48 shows the protection cir-
cuit schematic diagram.
Figure 5-48. External current bias protection circuit
Take caution of electrical shock hazards when using the external DC bias circuit.
A large energy is charged in L
1
and L
2
, as well as the DUT (Lx), by a bias current delivered from
an external power supply and when the DUT is disconnected from the measurement circuit, the
DUT generates a very high spike voltage (kick-back voltage) to discharge the energy. To ensure oper-
ator safety, decrease the bias current to zero before disconnecting the DUT.
L
1
and L
2
discharge through the protection circuit the instant the DUT is disconnected from the
measurement circuit or when the bias current is turned off. To prevent the instrument from being
damaged by harmful discharge, the protection circuit must be designed carefully for the withstand-
ing voltage/current rating of each circuit component. Refer to Application Note 346 A Guideline for
Designing External DC Bias Circuit for more information.
5-37