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[SOLVED] Voltage regulator beginner question

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Newbie level 2
Jun 17, 2011
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I'm totally new to electronics, so forgive me if this is some obviously silly question. I have purchased an XBee adapter which has a 5 to 3.3V voltage regulator for voltage input. Does this mean I can provide voltage anywhere between 3.3 to 5V? Or must I provide a 5V voltage? (e.g. Can I provide a 4.5V voltage tot he adapter with three 1.5V battery?

The data sheet for the XBee adapter can be found here:
**broken link removed**

This means you power up the board with 5V. It must be 5V or close to it. There is a voltage regulator on the pcb that outputs 3.3V that is used for your logic signals.

The datasheet says 3.3v on-board regulator and 5 V to 3.3 V logic translator buffers, the 5 to 3.3v has to do with the digital input level.
The Power Requirements are 5 VDC I don't think you should use a lower voltage and you may also have problems with the input buffers if you do.

Can you read the part number of the 3 terminal voltage regulator on the pcb? If so you can look up this datasheet and it will tell you the minimum voltage you are able to supply to achieve 3.3V output.
If the schematic is this


then the 74AHC125 buffer is powered with the 3.3v regulated supply so a lower voltage input supply shouldn't be a problem assuming that it is above the minimum input voltage for the regulator to output 3.3v.
In the schematics I found the regulator is shown as LM2937 (maybe yours is different so you have to check), if this is the case then it has a low dropout of 0.5v so you can use the 4.5v.

Thanks to your help, I'm able to complete the first step of my wireless sensor network (at least able to get the data out from sensors to internet, even though the sensor output do not seem correct at the moment). Seems like 4.5V input works! Many thanks! ^_^

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