Datasheet

Using The Line/Switcher Sense Output
LINE
INPUT
POWER
TRANSFORMER
FILTER
UC1903
UC2903
UC3903
www.ti.com ........................................................................................................................................ SLUS233A – OCTOBER 1999 – REVISED SEPTEMBER 2008
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
line/switcher input. By adjusting the R
2
C time constant with respect to the switching frequency of the supply and
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
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Product Folder Link(s): UC1903 UC2903 UC3903