13.8 to 7.5 power supply

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SCPD

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I want to run a 7.5VDC handheld from vehicle power.
Any thoughts the best/easiest way to do this?
 

rescue161

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gtriever

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He also wanted the best way, which a voltage divider is not. I'd start with a google search for a "battery eliminator" for his specific model handheld.
 

XTS3000

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Use a LM317 voltage regulator. It's a very easy circuit to build and you can set the voltage to a very precise 7.5V.

Rainbow Kits has a kit to make this simple voltage regulator for not much $$.

The LM317 can be configured as a voltage regulator OR a current regulator.

I recommend against using a voltage divider using 2 resistors because if your supply voltage changes, you output voltage changes as well. Voltage divider is unregulated circuit.

ImageUploadedByTapatalk1404482454.285917.jpg

Above is a my LM317 voltage AND current power supply for powering laser diodes. For a scanner, you would not need the 2nd current limiting LM317.

Another option I would do myself (but not recommend it to anyone else) is to simply use a LM7808 - 8V regulator. It's 0.5V higher than the scanner calls for, but scanners have their own built in voltage regulation circuits.
 

prcguy

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LM-317s were popular during the dinosaur era but today you can get a DC-DC switcher for about the same price as an LM-317. The drawback of a linear regulator like the LM-317 is if you need say 1 amp at 8v and your supply is 24v, it still draws about 1a from the 24v supply.

A switching regulator will supply the same 8v at 1a but the current draw from the 24v supply will be around 350ma or so.

Here is a source for switching regulator replacements for an LM-317 that is adjustable from 1.25 to 35v with an input voltage up to 40v and its assembled and tested for a buck each! New Mini 5X LM2596S 3A DC DC Buck Converter Step Down Module Voltage Regulator | eBay
prcguy
 
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n0nhp

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This is a bit of overkill but is one of the RF quietest switching regulators I have found.
Automatic Buck-Boost Module - Red (8A) - Free Shipping - DealExtreme
It is un-branded Chinese but they take Pay-Pal so you can contest the charge if you don't get what you ordered.
I have ordered a number of gadgets from them and the cheap ones are really cheap, the items like this one are pretty well made.
YMMV
Bruce
 
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