# 12v / 70amp into 3v Conversion

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 ?

Please Suggest me Suitable Circuit which is fullfill my requirement.

Thank You..

• LEDs run based on current so what you'd rather want is a constant current source – PlasmaHH Apr 22 '16 at 12:10
• 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. – kabZX Apr 22 '16 at 12:21
• @PlasmaHH the output requirement is stated as 3V, so I would assume that the "led light" needs a constant voltage input. – kabZX Apr 22 '16 at 12:22
• @kabZX: when was the last time you used a led with constant voltage sources? – PlasmaHH Apr 22 '16 at 12:23
• @PlasmaHH Of Course i have 3v led bulb. – Arsalan Arain Apr 22 '16 at 12:27

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.

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:

• Ah darn, forgot to put the LED there. It goes in before the transistor. – Barleyman Apr 22 '16 at 15:25
• @ArsalanArain You could always vote for it if you like it :-P – Barleyman Apr 22 '16 at 15:41
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:

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