Page 192 - Troubleshooting Analog Circuits

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Table 14.4 Troubleshooting Negative (Adjustable) Ragulrtors
Indication of Trouble Possible Cause Solution
Bad DC errors. Refer to table for
positive regulators,
above.
Oscillation. Refer to table for
positive regulators,
ALSO:
Improper C2 capacitor? Refer to manufacturer’s
data sheet: Avoid
ceramic or film caps.
Use tantalums or big
electrolytics.
Too many ceramic discs Swamp them with over-
connected on output bus? compensation, with tens
of FF tantalum, or a
few hundred FF
aluminum electrolytic.

Comments on Table for Negative (Adjustable) Regulators
These regulators have just about all the virtues and the freedom from problems as the
positive regulators, but they are quite critical about having a good capacitor from the
output to ground, as noted above.
The fixed negative regulators (LM320 family, LM7900 family) are likewise quite
demanding that a decent capacitor be used for the output’s damping. This is inherent
because the negative regulators all have collector-loaded outputs, and you need a
good capacitor to roll off the extra gain.

T. +V. - I

T

Vour

GROUND

Figure 14.5. LM723-Type Regulator.