12v To 3 Volt Resistor

There are a few things to consider when dealing with automotive circuits that are powered directly from battery. Most machine batteries operate at 12V nominally - but can sit anywhere betwixt 9V and 16V during normal functioning.

Consider this excursion (note Vbattery = 16V):

^{simulate this excursion – Schematic created using CircuitLab}

If your LEDs driblet ~3.5V and draw 100mA of current, you are burning .35Watts (Ability = Current x Voltage) in the LED - no big bargain. You still have 12.5V to drop somewhere else. In this case information technology across the resistor. Presistor = (16V - 3.5V) * 100mA = 1.25W. That'south quite a chip.

Nominal Calcluations (i.due east. Vbattery = 12V):

Pled = 3.5V * 100mA = .35W (same equally before)

Presistor = 8.5V * 100mA = .85W (still could be problematic)

I recommend going with this circuit, as to avert dealing with excessive voltage drib across one resistor. Be aware that if your battery drops very far beneath 12V, your LED string will probably shut off. 3.5V + iii.5V + 3.5V + Current*Rresistor = pretty close to 12V.

^{simulate this circuit}

Yous tin also spread the power dissipation across two resistors in each cord instead of just i. Each of these resistors will need to be half the resistance. See the schematic beneath.

Actress Credit: If you do desire a parallel LED application, you can try a more complex approach.

Another consideration is current matching, which isn't critical in most hobbyist applications but this arroyo volition also help spread out the power.

Consider this circuit:

^{simulate this excursion}

At the bottom of each string are BJTs. The left-most string has a BJT configured with the base of operations shorted to the collector - and the emitter to ground. All bases are tied together. This is called a electric current mirror every bit it forces the electric current in each of the strings to be the same. (I'k doing a lot of manus-waving hither. It's as well responsible to note that information technology isn't a guaranteed, perfect electric current lucifer between strings considering of thermal differences, process variations between BJTs, etc. - simply in this case it'south adept enough.)

What IS important here, is that yous can put a BJT that is capable of handling a bit of power to assistance you drop your voltage "more safely." Instead of putting a huge 2W resistor, you tin can get a niggling fancier and driblet some of the voltage across the BJT - decreasing the corporeality of power your resistors need to burn. It won't exist a whole lot. Y'all tin cull a BJT with a Vbe = 1V and drop .1W across the BJT (or a Vce = 2V and drop .2W). You lot also get the added benefit of ensuring your LEDs are all the same brightness.

Promise this helps!

12v To 3 Volt Resistor,

Source: https://electronics.stackexchange.com/questions/66348/im-trying-to-use-3v-leds-in-a-12v-circuit-in-my-car

Posted by: garcialadiandal.blogspot.com

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