I have a question about supplying a LED circuit (2 parallel branches of LEDs, each branch with 2 LEDs and a ballast R) with a voltage lower than the Vforward of the LEDs.
LED Vforward range of 1.90 - 2.85 through all temperature ranges.
In this case the circuit has one branch with LED Vf on the lower end of the range (1.90*2 = 3.8) and one branch with LED Vf on the upper end of the range (2.85*2 = 5.7). Both branches have a 13Ohm ballast to evenly distribute the current regardless of Vf. The target current for the circuit is 50mA so each branch would have 25mA. The objective is to test functionality of the strings by applying a voltage and checking current.
IR + Vf = Vin gives me 2 Vin values for the range of Vf.
for Vf = 1.90, Vin = 4.125
for Vf = 2.85, Vin = 6.025
The problem is that I can only use 1 Vin. If I use 6.025 then any circuit with Vf = 1.90, the LEDs will be driven past their current rating and risk damage to the LED.
If I use 4.125 then any circuit with Vf = 2.85 will not have enough voltage to fully forward bias the LEDs.
All that being said, if I under drive the circuit with say 3VDC, will the current be the same throughout the Vf range. I understand that the luminance of the LEDs will be lower but that is not the target of the test.
Thanks for reading through and I look forward to any responses.
LED Vforward range of 1.90 - 2.85 through all temperature ranges.
In this case the circuit has one branch with LED Vf on the lower end of the range (1.90*2 = 3.8) and one branch with LED Vf on the upper end of the range (2.85*2 = 5.7). Both branches have a 13Ohm ballast to evenly distribute the current regardless of Vf. The target current for the circuit is 50mA so each branch would have 25mA. The objective is to test functionality of the strings by applying a voltage and checking current.
IR + Vf = Vin gives me 2 Vin values for the range of Vf.
for Vf = 1.90, Vin = 4.125
for Vf = 2.85, Vin = 6.025
The problem is that I can only use 1 Vin. If I use 6.025 then any circuit with Vf = 1.90, the LEDs will be driven past their current rating and risk damage to the LED.
If I use 4.125 then any circuit with Vf = 2.85 will not have enough voltage to fully forward bias the LEDs.
All that being said, if I under drive the circuit with say 3VDC, will the current be the same throughout the Vf range. I understand that the luminance of the LEDs will be lower but that is not the target of the test.
Thanks for reading through and I look forward to any responses.