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12v to 1.5v coverter

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ferez

New Member
hi ya all

i want to put my mp3 player in my car and supply it a constant voltage of 1.5v (it consumes very small amount of ampere).

how can i build a circuit that will give me a voltage of 1.5 DC out of the car's battery 12v (the actual voltage is between 12-13.8) DC?

tnx and good day :)
 

Gordz

New Member
National Semiconductor / Fairchild do an SOT-23 sized 1.5 volt LDO and they are pretty cheap. Your MP3 should run fine off 1.2v so use two diodes and a resistor for a really simple regulator.
 

mvs sarma

Well-Known Member
As Ferez has indicated it s consumption is LOW, the best thing is to leave it on its battery and make best use of its portability, rather thanrisking all these trials.

If ore power is needed better to adopt a D cell by external implementation and it will be stomach full for a month , i suppose.
 

blueroomelectronics

Well-Known Member
mvs sarma said:
As Ferez has indicated it s consumption is LOW, the best thing is to leave it on its battery and make best use of its portability, rather thanrisking all these trials.
Most senseable answer yet. A decent NiMH will run for hours and not damage your MP3 player.
 

ferez

New Member
hi guys, first of all i want to thank ya'all for the answers.
second thing, the MP3 player can't be feed through a regular battery because it will be molded\glued to my dashboard (i need to make it look like a built-in gadget in the dash).

so, what is the best solution? the LM317?
 

mvs sarma

Well-Known Member
adopt a cellphone charger with 5v output from the car battery- then use aa LM317 adj pin grounded and you will get 1.2v volts output. mostly, this is sufficient for the mp3 player.

first make dummy load trial outside and then use it for the regular device.
 

CynicalMan

New Member
Roff said:
That will result in 7.1V, and probably smoke from the MP3 player. You have reversed the values. The desired values are R1=220, R2=47.
OOPS!!! Sorry if I caused any damage:eek::eek::eek:
 

Hero999

Banned
mvs sarma said:
adopt a cellphone charger with 5v output from the car battery- then use aa LM317 adj pin grounded and you will get 1.2v volts output. mostly, this is sufficient for the mp3 player.

first make dummy load trial outside and then use it for the regular device.
You still need a resistor on the output as it has a minimum load requirement of 10mA so it won't regulate properly if you MP3 player uses less than that.
 

mvs sarma

Well-Known Member
ferez said:
sorry for the stupid question but, how do i make a dummy load? what is the dummy load consists of?
HERO999 is very much correct for the minimum load requirement.
Try putting one red LED with a series resistor of say 82 to 100 ohms and connect across the common ground and +3.3V output. this will work as artificial load (so called dummy load) . Artificial load could also be a 150 resistor but you won't know unless you measure. In the other case, the LED glows. how ever you can calculete the resistor value to suite 70% of maximum permitted current for the RED LED.generally Red LED drops 1.4V across it in the forward direction thus series resistor would be (3.3-1.4)/permitted current for the LED.
 

Diver300

Well-Known Member
Most Helpful Member
As the current is really small, and you only need it when the radio is on, I suggest a shunt regulator. You can use two diodes in series which will give around 1.3 V. You should add a series diode to make sure that reverse polarity won't damage anything.

Shunt regulators are the least efficient, but efficiency isn't important in this application. Shunt regulators are also very robust and won't die if there is a voltage spike.
 
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