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I have a battery 12v / 70amp & i want to convert into 3v for small led light. Is this circuit is suitable for my voltage requirement ?

enter image description here

Please Suggest me Suitable Circuit which is fullfill my requirement.

Thank You..

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    \$\begingroup\$ LEDs run based on current so what you'd rather want is a constant current source \$\endgroup\$ – PlasmaHH Apr 22 '16 at 12:10
  • \$\begingroup\$ What is your load current requirement? The circuit you have made will certainly work. The load current will determine the (heat) loss in the transistor. \$\endgroup\$ – kabZX Apr 22 '16 at 12:21
  • \$\begingroup\$ @PlasmaHH the output requirement is stated as 3V, so I would assume that the "led light" needs a constant voltage input. \$\endgroup\$ – kabZX Apr 22 '16 at 12:22
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    \$\begingroup\$ @kabZX: when was the last time you used a led with constant voltage sources? \$\endgroup\$ – PlasmaHH Apr 22 '16 at 12:23
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    \$\begingroup\$ @PlasmaHH Of Course i have 3v led bulb. \$\endgroup\$ – Arsalan Arain Apr 22 '16 at 12:27
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You don't need the complication of a linear regulator; just use a resistor. The LED will take (say) 50mA at 3V - that's an equivalent resistance of 60 ohms. Make a potential divider with a 2nd resistor up to 12V. That 2nd resistor will drop 9V at 50mA i.e. it will be a 180 ohm, 0.5 to 1 watt resistor.

Ratio up or down the resistor value with current actually needed and check the power dissipation.

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That circuit is a huge overkill for a simple LED. Lose all of the capacitors.

We don't know the specification of "3V" LED so I presume it refers to forward voltage. So in other words, you have 12-3 = 9V to deal with.

If you want 20mA (check LED spec), R = U/I => 450R which is about the same as 470R. Bear in mind that you get 9V * 20mA = 180mW power loss over the resistor so you need 1/4W resistor or better.

If you have your heart all set to a transistor current controller, you need to do a bit more work. This would work:

enter image description here

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  • \$\begingroup\$ Ah darn, forgot to put the LED there. It goes in before the transistor. \$\endgroup\$ – Barleyman Apr 22 '16 at 15:25
  • \$\begingroup\$ @ArsalanArain You could always vote for it if you like it :-P \$\endgroup\$ – Barleyman Apr 22 '16 at 15:41
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  1. Get rid of everything except the battery, the LED, and the resistor.
  2. Connect the battery, the resistor and the LED in series, like this:

enter image description here

  1. Mind that you don't connect the LED backwards.
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