How to step down 12vDC to 6vDC

Discussion in 'Electronic Projects' started by VirtualMonitoring, May 27, 2010.

  1. VirtualMonitoring

    VirtualMonitoring

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    I'm not into electronics, but I think this one is so easy I should understand most of the answers (hopefullly).

    Here is my situation:

    My company provide a service to people who have Linksys VoIP adaters which are powered by 6vDC. They use them to send alarm signals to a monitoring center, so it would be better if the Linksys could be powered from the alarm panel and take advantage of the battery backup in case of power failure. The problem is, all alarm panels are 12vDC - or thereabouts.

    I have been searching for months hoping to find a simple PCB with two 12v input terminals on one side and two 6v output terminals on the other. I've just about given up, so I'm wondering if any of you guys would know of something along those lines ?
     
    VirtualMonitoring, May 27, 2010
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  2. VirtualMonitoring

    Mitchekj VIP Member

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    Two inputs, two ouputs? Any reason they would need to be separate? What kind of current are we talking about?

    In any case, 12Vdc to 6Vdc is easily done. Either linear or switching, depending on what exactly it is you need in the way of efficiency, regulation, etc.
     
    Mitchekj, May 27, 2010
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  3. VirtualMonitoring

    LTX71CM VIP Member

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    How much current at 6v would you require? A few hundred milliamps, 1 amp?
     
    LTX71CM, May 27, 2010
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  4. VirtualMonitoring

    VirtualMonitoring

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    Here is what I am trying to do... http://www.ipalarms.net/pap2.htm

    The two inputs are for connecting the alarm panel 12v. The two outputs are for connecting to the Linksys device.

    I think most alarm panels can fluctuate between 11-17vDC and the 6v to the Linksys needs to be regulated. Does that make it more complicated....and expensive ?
     
    VirtualMonitoring, May 27, 2010
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  5. VirtualMonitoring

    VirtualMonitoring

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    I checked the spec. Good job because I was wrong about the voltage...

    ● DC input voltage: +5V DC at 2.0A max.
    ● Power consumption: 5W
    ● Switching type (100–240V) automatic
    ● Power adapter: 100–240V - 50–60 Hz (26–34 VA) AC input, 1.8 m cord

    I think we have problems as many alarm panels only output 1 amp.
     
    VirtualMonitoring, May 27, 2010
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  6. VirtualMonitoring

    LTX71CM VIP Member

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    LTX71CM, May 27, 2010
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  7. VirtualMonitoring

    Mitchekj VIP Member

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    Personally, I'd spec something with a 3 to 4A+ rating, but I like to play it safe... it says 2A max input, but does it go a little higher somtimes? The LDO says 2A, but is that specmanship? No one can be sure. :)

    Anyhow, you don't need an LDO if you're going for cheap. Any old linear regulator would work, so long as it's rated properly.
     
    Mitchekj, May 27, 2010
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  8. VirtualMonitoring

    VirtualMonitoring

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    Thanks - that component looks very interesting. Excuse my ignorance, but is it as simple as connecting 4 terminal blocks to the 4 legs of the component and then connecting the 12v supply to two of them ?

    This would then give me a regulated 5v output ?

    By the way - no I can't read schematics, they are always in Chinese ;-)
     
    VirtualMonitoring, May 27, 2010
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  9. VirtualMonitoring

    LTX71CM VIP Member

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    Mitchekj the regulator can handle up to 15W with heatsink, I think it would be ok (provided a heatsink is used). At less than $1 I doubt price would be an issue. Don't forget this will be a battery powered system when the mains is out.
     
    LTX71CM, May 27, 2010
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  10. VirtualMonitoring

    LTX71CM VIP Member

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    VirtualMonitoring, no, it's not that easy but it is easy. One pin is ground, one is 12V in, one is 12v out and the final pin is for adjusting the output voltage with a resistor based voltage divider.

    Why do you need two 6v outputs? Two devices? Just use two jacks connected to the same output.
     
    LTX71CM, May 27, 2010
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  11. VirtualMonitoring

    Mitchekj VIP Member

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    Unfortunately it isn't quite that simple, VirtualMonitoring. You'd need to add a few more components to set the output voltage, provide some decoupling, etc. And as LTX71CM said, heat sinking will be required.

    I would use the LM350 (http://www.fairchildsemi.com/ds/LM/LM350.pdf) myself, but there are many others that would work. (Again, I'd shy away from something rated at exactly 2A, regardless of power rating.)

    What are the two input/output requirements? Does it need two distinct voltage sources, or can it use one in, two out, etc? Is the 2A rating per output, or total? The regulator that LTX71CM recommended would work nicely if it's 1A per output.
     
    Mitchekj, May 27, 2010
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  12. VirtualMonitoring

    VirtualMonitoring

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    Thanks for your help. I now realise that my alarm installer terminology is not helpful to an electronics guy, so I'll try to explain.

    When I say two output terminals, I mean two terminal block connections. One of them 0v and one of them 5v - so it's a single, two-wire output.

    Anyway, I was looking for an assembled "off the shelf" product at this stage, so even though I will keep that component on record, it will not solve my immediate problem.
     
    VirtualMonitoring, May 27, 2010
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  13. VirtualMonitoring

    LTX71CM VIP Member

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    LTX71CM, May 27, 2010
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  14. VirtualMonitoring

    Mitchekj VIP Member

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    That works. :) Nice find LTX.
     
    Mitchekj, May 27, 2010
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  15. VirtualMonitoring

    VirtualMonitoring

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    Now I'm excited ;-)

    At first look, that seems to be exactly what I am looking for. Thank you so much you guys.
     
    VirtualMonitoring, May 27, 2010
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  16. VirtualMonitoring

    LTX71CM VIP Member

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    Thanks, not too bad a price either considering the others I found searching.

    Glad we could help.
     
    LTX71CM, May 27, 2010
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  17. VirtualMonitoring

    Resqueline Moderator

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    I see you worked it out and found a real nice switchmode regulator. (Gee, you folks work fast..) That's preferable to a linear regulator because:
    Power dissipation can be an issue. Also, will the alarm system be able to deliver 1A more continously and 2A peak?
    Dissipation in the linear will be 1A*(14.5V-5V)=9.5W continous, 19W peak. That's going to take a substantial heatsink to get rid of.
    With the switchmode regulator the 12V current draw will be only (5W/0.9)/14.5V=0.38A and its dissipation will be only 0.5W. No need for heatsinking.
    Good work. :)
     
    Last edited: May 27, 2010
    Resqueline, May 27, 2010
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