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I am trying to get a fixed 5V output from an inductive proximity sensor. The proximity sensor comes with 3 wires: bn(V+), bu(V-), and bk. A wiring diagram can be seen here on page 2/12. I have available to me both NPN and PNP style sensors and have tried using both.

I am having trouble figuring out why it does not work with a LM2576 though. I am powering the inductive prox sensor's connectors with +24V to bn(V+), bu(V-) to common, and bk to the input of the LM2576 which is then supposed to give a 5V output. I have the bk going into pin 1 of the LM2576 and everything else connected similar to Figure 1 in the LM2576 datasheet. Can anyone give me insight as to why when I connect the bk wire of the prox sensor to the input of the LM2576 it does not output 5V?

I have already verified that all components work by setting them up in other says (such as providing direct power to the input of the LM2576 and verifying it outputs 5V).

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The LM2576 needs a high current path for the input.

You can't run the wimpy output of a prox sensor into the input and expect it to work.

Connect the LM2576 input directly to your 24V supply.

temporarily ground pin 5 (ON/OFF) and verify that the power supply is actually delivering +5V.

Then disconnect pin 5 from ground and attach it to the bk wire of the NPN version of the sensor.

That should allow the +5V output to be controlled by your sensor.

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  • \$\begingroup\$ Thanks for the insight. I'm about to go try it out so hopefully it works fine. I have the output going as an input to a microcontroller that is trying to track if the LM2576 output is on or off. (Not a school project) \$\endgroup\$ – Maarij Oct 3 '13 at 20:37
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If you only want to limit the sensor's output to 5 volts to feed a microcontroller input, it seems to me that using a switching regulator like the LM2579 is a serious misapplication of inappropriate technology.

I might suggest a resistor and 4.7 volt zener diode, or an LM78L05, since the microcontroller input will require essentially no current.

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