30
OPERATING PRINCIPLE
TOS8870A
[13] Current detection circuit
Consists of a current detecting resistor, a reference voltage generator circuit, and a comparator.
[14] Control circuit
Controls overall operations of the Tester. Structured in high-reliability logic circuits with CMOS
IC.
[15] Protective circuits
Various protective features are incorporated for the safety of tests. But be careful to operate.
[16] Window comparator
Generates a PASS signal only when the leakage current is within the range between the high limit
reference value set with the CUTOFF CURRENT switches and the low limit reference value set
with the LOWER REFERENCE value control. When the leakage current is not within the above
range, the comparator generates a FAIL judgement.
4.3 Zero-Start Switch
If a regular mechanical contact type relay is used for on-off operation of the primary circuit of the
high voltage transformer, transiential spike voltages could be produced, thereby applying an unjus-
ti
fi
edly high voltage to the device under test (DUT) and causing a possibility of re-jecting an
acceptable DUT. The zero-start switch, which employ a solid-state switching circuit, turns on and
off the power line at approximately 0 V level, thereby reducing transiential overshoots.
Fig.4-2
START signal
STOP signal
TEST ON signal
Test voltage waveform
when mechanical
relay is used
Test voltage waveform
when zero-start
switch is used
