Do i need a transistor for my LED's?

[Ferrariassassin]

I will be modding my PS4 controller with 4 3mm Blue LED's powered by a 2000mAh 3.7v battery in the controller. DO i need a transistor to stop the LED's from frying or will 3.7v not hurt them? The Batter i have and LED's i bought are below. If i do need a transistor can someone link me some i need, thanks

https://www.amazon.com/CHANZON%C2%AE-100pcs-colors-Emitting-Assorted/dp/B01AUI4W5U/ref=sr_1_1?ie=UTF8&qid=1469067340&sr=8-1-spons&keywords=3mm+led&psc=1

https://www.amazon.com/gp/product/B00RHD2CL8/ref=ox_sc_act_title_2?ie=UTF8&psc=1&smid=A1S9OMG83CAC4S

 

[Pinhedd]

I will be modding my PS4 controller with 4 3mm Blue LED's powered by a 2000mAh 3.7v battery in the controller. DO i need a transistor to stop the LED's from frying or will 3.7v not hurt them? The Batter i have and LED's i bought are below. If i do need a transistor can someone link me some i need, thanks

https://www.amazon.com/CHANZON%C2%AE-100pcs-colors-Emitting-Assorted/dp/B01AUI4W5U/ref=sr_1_1?ie=UTF8&qid=1469067340&sr=8-1-spons&keywords=3mm+led&psc=1

https://www.amazon.com/gp/product/B00RHD2CL8/ref=ox_sc_act_title_2?ie=UTF8&psc=1&smid=A1S9OMG83CAC4S

It's not the voltage that will kill the LED, it's the current. LEDs are non-linear devices, they must have a linear resistor in series to limit the current. Most LEDs 3mm should be limited to 20 milliamps to prevent damage. A 3.7 volt Lithium-Ion battery will deliver far, far more than that.

You'll need to find the forward bias voltage of the LED and find a current limiting resistor (not tranisistor) that will keep the loop current at or below 20ma when using a supply voltage of 3.7 volts.

 

[PhysX_HW]

the blue LED needs 3.0V at 20mA, so the voltage across the resistor will be 0.7V. Since R=V/I, R=0.7V/0.020A. You will need approx. 35ohm resistors, but only small ones, like 0.125W or less. One for each LED.

Like these:
http://cpc.farnell.com/multicomp/mf12-39r/resistor-0-125w-1-39r/dp/RE04954