I'm trying to figure out how to determine the forward voltage and forward current for overdriven LEDs, and need a bit of help understanding what are the dependent variables and which are independent variables.
For a normal 3mm LED, I understand that I'd set the forward current by looking at the typical forward voltage (usually between 2.0 and 3.5 volts or so), the typical forward current (usually 20-25 mA), and the supply voltage. I'd calculate the remaining voltage and then divide by the desired current to get a resistance value; usually I find these to be like 100-200 ohms or so with a 5V supply.
The problem that I'm working with now is that I'm attempting to overdrive LEDs by a factor of 50x-100x (so, running up to 2 amps through an LED in 100 us pulses, for a duty cycle of 0.01%). I've seen papers suggesting that this should be possible, but I'm having trouble figuring out how to compute the resistance values.
I'm using a circuit, as shown below, to drive the LEDs:
The supply voltage is around 12 Volts, so the capacitors charge up to 12 volts, and then dump current through the LEDs. I want a resistor R2 to regulate the current and provide me a way to measure the current going through the LEDs.
I'm having trouble figuring out what the resistor value should be, because the forward voltage and forward current are both related -- if I try to drive them beyond their "typical" current, the forward voltage should comparatively increase.
The I-V curve for these LEDs is as shown below:
I feel like I'm in a bit of a chicken and egg scenario, where I don't know how to find the forward voltage without knowing the current, or the current without knowing the forward voltage.
How should I approach deciding the value of resistor R2?