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Voltage Limiting

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Rookie ( offline )
Posts: 43
Posted: 2008-04-29 16:01 
 Post subject: Voltage Limiting

My current project requires that I step 12V down to 7.5V to power a wireless router. I have never done anything like this before and am a little nervous about it. Just need a little help.


Guru ( offline )
Posts: 2158
Posted: 2008-04-29 19:41 
 Post subject: Re: Voltage Limiting
what current (in amperes) or power (in watts) does the router require? voltage is only half of the information required to determine what type of regulator or converter is necessary.

Rookie ( offline )
Posts: 43
Posted: 2008-04-29 23:58 
 Post subject: Re: Voltage Limiting
Ohh yeah that could be useful.

The router wants 1 amp. An I am using a 12V battery to power it so i am not worried about not enough power just to much.

Thanks for the help.

New ( offline )
Posts: 3
Posted: 2008-04-30 02:47 
 Post subject: Re: Voltage Limiting
Have you opened the router and had a look at its power supply section? If it is using a linear converter such as a 7805, which sounds likely based on the 7.5V input requirement, you can connect it directly to the 12V supply.


Novice ( offline )
Posts: 74
Posted: 2008-04-30 06:47 
 Post subject: Re: Voltage Limiting
That would mean the 7805 has to dissipate 7 Watts as opposed to 2.5 Watts, significant difference :wink:

Ok wait... that part isn't supposed to be smoking..

Guru ( offline )
Posts: 2158
Posted: 2008-04-30 10:04 
 Post subject: Re: Voltage Limiting
ScuD has a good point. To use a linear regulator like a MC78M08 or LM317T (adjustable, set to 7.5V) you will need to be able to dissipate roughly 6W from the device (input to which could actually range from 13.8V to 10V or so if using a 12V battery). You also may want to consider that if running from a battery the efficiency of the regulator might be important. This all suggests a small dc-dc converter or switching regulator circuit might be a good idea. Has anybody seen any R/C switching BEC devices that output other than 5V or 6V?

Rookie ( offline )
Posts: 43
Posted: 2008-04-30 11:00 
 Post subject: Re: Voltage Limiting

Thanks for the interest.

The router is powered by a wall wart transformer:

MODEL NO:AM-0751000D41
INPUT:120VAC 60 Hz 15W
OUTPUT 7.5VDC 1000 mA

The router is a D-Link DI-524:

Where the plug from the transformer goes in to the casing 7.5V = 1A is stamped on it. On the inside the terminal is wired right onto the board.

Thanks again guys.

PS just thought of something could it be possible to run it on 6V instead of 7.5? Is there a danger in doing so with an electrical device like this?


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