Step down voltage regulator not working with inductive prox sensor

Question

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).

Answer 1

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.

Answer 2

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.