Using The Line/Switcher Sense Output

LINE

INPUT

POWER

TRANSFORMER FILTER

UC1903

UC2903

UC3903

The line switcher sense input to the UC1903 can be used for early detection of line, switcher, or other power

source, failures. Internally referenced to 2.0 V, the line sense comparator will cause the POWER OK output to

indicate a fault (active low) condition when the LINE/SWITCHER SENSE input goes from above to below 2.0 V.

The line sense comparator has approximately 175 mV of hysteresis requiring the line/switcher input to reach

2.175 V before the POWER OK output device can be turned off, allowing a no-fault indication. In Figure 7 an

example showing the use of the LINE/SWITCHER SENSE input for early switcher-fault detection is detailed. A

sample signal is taken from the output of the power transformer, rectified and filtered, and used at the

the hold up time of the output capacitor, switcher faults can be detected before supply outputs are significantly

affected.

Figure 7. Line/Switcher Sense Input Used for Early Line or Switcher Fault Indication

Copyright © 1999–2008, Texas Instruments Incorporated

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Product Folder Link(s): UC1903 UC2903 UC3903