Circuit Review Request - Buck Converter

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I’m building an Arduino Micro + BLE sensor shield. The shield will hold these sensors:

  1. Temperature - LM35

  2. Differential Pressure - http://www.allsensors.com/products/30INCH-D1-P4V-MINI

  3. Barometric Pressure - http://www.allsensors.com/products/15-psi-a-4v-mini1

My supply power is 4-AA batteries, which should draw down between 6V and 5.2V. I want to run the pressure sensors between 4.5V - 5.5V, and also power the Arduino + BLE (http://redbearlab.com/blendmicro/) at that same voltage.

I’ve modeled a transistor, diode, capacitor, resistor Buck converter circuit, and have attached screens of the LTSpice runs (as well as the Spice sketch).

I’d appreciate any help in reviewing this circuit to help me make sure I’m not over-looking anything. The 1K load is likely not realistic, but I don’t have the sensors currently in-hand, and just received the Arduino board yesterday, so I can’t think of how to better estimate it.

Thanks!

Bob