Download Troubleshooting Techniques

Troubleshooting Techniques
Troubleshooting Op-Amps (Cont’d)
Internal Failures in Comparator circuits
External Component Failures in Comparator circuits
R1 and R2 set the UTP and LTP for the hysteresis
comparator. When the R2 open, all of the output
voltage is fed back to the noninverting input. Since the
input voltage will never exceed the output, the device
will remain in one of its saturated states.
When R1 open, this leaves the noninverting input
near ground potential and causes the circuit to
operate as a zero-level detector.
0V
Quick Check for a Comparator
Quick Check for a Comparator with Hysteresis
Symptom: Comparator circuit doesn’t seem to work
Symptom: Schmitt trigger circuit doesn’t seem to work
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Temporarily connect jumper J1 or J2, to force the
comparator from its current state to the opposite
rail voltage.
If you can’t force the comparator into the alternate
state, check the power-supply voltages and the
voltages in the reference-voltage circuit. Another
possibility is that the IC is bad.
Verify that the reference voltage is correct.
If the reference voltage is okay, and if it is possible
to force the comparator into the alternate state,
then the comparator is okay, and the likely problem
is with the input signal.
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•
Temporarily connect jumper J1 or J2, to force the
comparator from its current state to the opposite
rail voltage.
If you can’t force the comparator into the alternate
state, check the power-supply voltages and the
components in the positive-feedback circuit.
Alternatively, the IC may be bad.
If the positive feedback circuit is okay, and it is
possible to force the comparator into the alternate
state, the comparator is okay and the likely
problem is with the input signal.