Auxiliary Power Option B (Rear Aux or RAUX Pin Method)
In the following discussion, pay close attention to Fig. 14.6. Application of Rear Aux can be very useful, but also confusing.
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FIGURE 14.6   Rear Aux method in more detail.
Rear Aux has the following advantage from a heuristic viewpoint: it introduces the ability to cause the PSE to disconnect power if desired, by just turning the pass-FET of the front end (“Q1”) OFF. If the PSE current then falls below 5 mA, the PSE will typically disconnect, though it will likely keep attempting detection. ...

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