performance of the tantalum will be better. There should also

be large supply reservoir capacitors of about 4700 µF on

each supply rail. A larger reservoir capacitor will reduce the

supply ripple and will supply larger current burst require-

ments instead of requiring those large currents to come from

the main power supply transformer.

If adequate bypassing is not provided, the current in the sup-

ply leads, which is a rectified component of the load current,

may be fed back into internal circuitry. This signal may cause

signal distortion to increase.

Layout and Ground Loops

When designing a printed circuit board layout, it is important

to return the load ground, any output compensation ground,

and the low-level (feedback and input) grounds to the circuit

board common ground point through separate paths. Large

currents flowing along a ground conductor will generate volt-

ages which effectively act as signals to the input ground ref-

erence. This can result in high frequency oscillation or ex-

cessive distortion. Output compensation components and

the high frequency supply bypass capacitors should be

placed as close as possible to the IC to reduce the effects of

PCB trace resistance and inductance. For cases where long

traces must exist, widen the traces to minimize their induc-

tance.

References

International Electronic Research Corporation

P.O. Box 7704,

Burbank, California 91510-7704,

(818) 842-7277

Thermalloy Inc.

P.O. Box 810839,

Dallas, Tx 75381-0839,

(214) 243-4321,

www.thermalloy.com

www.national.com

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