TOS8870A
OPERATION PROCEDURE
15
Detection small leakage currents
The window comparator system is especially advantageous when the leakage current values
of DUT are not distributed widely and are larger than the minimum detectable current of the
Tester. To test such DUT, the low limit reference (LOWER REFERENCE) value may be set
at a value slightly smaller than the predicted lowest value, and the test may be done in the
window comparator system. When this is done, DUT of exceptionally small leakage currents
can be identi
fi
ed and open-circuiting of leadwires and imperfect contacting also can be
detected, thereby substantially facilitating the withstanding voltage test.
Tests with low limit judgements for low leakage currents will be inconvenient when setting
the test voltage in the no-load state or when the DUT draw almost no current. In such cases,
set the LOWER ON/OFF switch to the OFF state to disable the low limit judgement function.
Judgment errors by stray capacitances
When test is made with a high sensitivity using a high AC voltage, it is possible that the cur-
rent which
fl
ows through stray capacitances of the test leadwires and other DUT becomes
larger than the low limit reference value and no low limit judgement for low leakage current
can be correctly made. That is, when the DUT is disconnected from the test setup, a FAIL
judgement should be made since the current drawn by the DUT is zero and is absolutely
smaller than the low limit reference value. Actually, however, since the current which
fl
ows
through the stray capacitances is larger than the low limit reference value, the Tester errone-
ously generates a PASS judgement signal. Refer to the *3 in Chapter 7 "SPECIFICATIONS"
on page 37.
Pay attention to this type of judgement errors. Make it sure that the Tester correctly makes
FAIL judgement when the DUT is disconnected from the test setup.
11) Setting the LOWER REFERENCE value
To set LOWER REFERENCE, use a trimming screw driver, etc.
1.
Set the high limit reference value (CUTOFF CURRENT value).
2.
Set the TIMER ON/OFF switch to the OFF state.
3.
Set the LOWER ON/OFF switch in the OFF state.
4.
Turn the LOWER REFERENCE value control to the counterclockwise position.
5.
Connect the DUT as described in "6) Connecting the DUT".
6.
Make settings as shown in the
fl
