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Problem with Low current ...

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Rdj

New Member
Hello, I wanna help, my modem d-link run with 12v, 0.5A ,,, i have power supply with 48v , i want use it to run my modem, i use voltage regulator l7812cv , it convert 48v to 12v , 1A , but modem doesn't run i think the source current is too low therefor modem does not run , so how can boost or amplify current without change in voltage .
 

spec

Well-Known Member
Most Helpful Member
Hi Rdj,

the linear regulator you are using can only supply 1.5 Amps maximum, but with a 48V input the regulator would only be able to supply about 0.028A without a heatsink and perhaps 0.139A with a fair sized heat sink.

Instead of a linear regulator, a switch mode regulator would be far more appropriate.

There are a heap of suitable switch mode regulators on the net, especially eBay: http://www.ebay.co.uk/itm/Waterproof-DC15-55V-48V-36V-24V-to-12V-3A-36W-Converter-Step-Down-Regulator-car/121807199193?_trksid=p2141725.c100338.m3726&_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=20150313114020&meid=aa8f5480ee1a4f518d6ecdf75d55ff08&pid=100338&rk=5&rkt=29&sd=221976123578

spec

DATASHEET
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00000444.pdf
 
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Rdj

New Member
Thanks 4 reply ... Ok can add resistor to circuit before regulator to step down voltage at least 35v then to l7812cv to boost current ? Or i hear about " tip2955" that amplify current ?
 

audioguru

Well-Known Member
Most Helpful Member
A series resistor only reduces the voltage when there is some current. The current used by the modem might vary so much that the voltage regulator will frequently have an input voltage high enough to destroy it.
If you adds a transistor to boost the current then the regulator will still get an input voltage that is too high.
A 12VDC/0.5A power supply is common and cheap. Get one.
 

Rdj

New Member
Thanks audioguru, yup i know about converter step up and down , I'm Architect engineer electronic is my hobby , i want create by my self any way thanks for reply ...ok i have a question , if we see data sheet of 7812 regulator , it say out put current about 1.5A , i think current source too much low therefor out put current less than 0.5A therefor modem does not run ... My question is that ? Is any way to boost current with out change in voltage ?
 

audioguru

Well-Known Member
Most Helpful Member
Can your 48V supply produce 0.5A?

The 7812 is either damaged by your input voltage being much too high or the 7812 is reducing its output current or even shutting down because its very high input voltage is causing it to heat too much.
A 7812 can power a device with an extremely small current perfectly, if its input voltage is reasonable.
 
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