Page 195 - Troubleshooting Analog Circuits

I 82 14. Real Circuits and Real Problems

Comments on Table for Full-wave Rectifiers
As with other complicated circuits, if you have to keep a circuit even as complex as
this in production, you should have a breadboard all built up, with sockets for any
critical components, to make it easy to evaluate them at a minute’s notice. Otherwise
you may just try to duck the problem, and that would be wrong.

-VIN
ca
7+
R5

Figure 14.7. Instrumentation Amplifier.

Table 14.7 Troubleshooting Instrumentation Amplifiers
Indication of Trouble Possible Cause Solution
Input stage works badly. Anything? Ground one input and put
a signal in the other
input; troubleshoot as
inverting amplifier.
Then swap inputs.
Bad output stage? Ground one input of output
stage and put a signal in
the other; troubleshoot as
above.
Bad DC errors. Anything? Ground both inputs; read
all voltages with DVM,
remove suspected bad
amplifier and test.
Bad CMRR. Input stage? Tie both inputs together
and drive + and -. Read
all voltages. Check
input op amps’ CMRR.
Output stage? Check resistors’ match
and trim range. Check
output op amp.

Comments on Table for Instrumentation Amplifiers
As above, this circuit should be set up with sockets for ease of evaluation. This cir-
cuit does offer a little more interaction, but it is not really too difficult when you
figure out what has to be going on.