Using Voltage Regulators with batteries

I had a question on using voltage regulators and I was hoping someone could help me,
I plan on using some batteries to power my circuit which is two different LEDs in parallel. I was wondering if I am right in wanting to use a voltage regulator to keep the input voltage constant (as the batteries will discharge over time I believe) for my LEDs but now I am curious as to how I will get the correct current input into those LEDs. They need 20mA and 13mA I believe and both the LEDs need the same voltage to operate.
Would those LEDs just pull the current they need as the regulated voltage will be the minimum voltage they need?


Well generally LEDS are current driven devices. A bettery will last a long time powering two LEDs. Though it would depend on the circuit and how long it is going to need to function. Unfortunately LEDs do not pull the current needed. They do need the recommended current to do the full output. Voltage can vary a little bit and even be less. Though you do need to put the recommended voltage. There is usually a range listed with the minimum and maximum voltage. I have used less in some cases, but kept the current to the recommended value . Less voltage will work. I would recommend using the correct current that is recommended on the data sheet.

Thank you for the quick reply,
Yes they will be running for quite a while, if I were to select a slightly higher output voltage then could I use a small resistor to make sure the current I need is allowed?
For example if I had a source of 4.5V then regulated it down to 3.5V and then used a resistor and Ohms law to get to the current needed? Knowing the LEDs want 3 V meaning .5V is left over and use a 25 ohm resistor for the first LED and about a 40 ohm one for the other one?

I think that should be okay. You can use slightly more or less voltage. Voltage is not as critical. You just do not want to use a lot over. Slight differences in voltage should be okay. Now current you want to stay close. The reason is if you use more, you will not get the hours that you should out of them. A little less might be okay, it just will not get as bright. Though it could last longer.

Okay sweet good to know, so use slightly larger resistors to lower that current draw and increase the life?
Also for capacitors, should the ones in the spec sheets be used or not since you were saying voltage doesn’t matter as much, could I get away with just regulators ability?

The LED can draw the correct current value. Though it can be less if you do not care if it is not as bright. It does extend the life of the LED. The voltage can’t be so low that the LED will not light. Though they generally give the minimum and maximum ratings on the data sheet. If you are using a regulator and they are recommending values for the capacitors, I would use what is recommended so it works.

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