Hello,
Do you know that is it possible to obtain pulsewidth of 100 ns with the EPC9150 Laser driver Board? For the formula of the pulsewidth related to the capacitor and inductor :
tres = 2π√((L1C1)) = 2twb
with the same inductance ( PCB + Laser ), if the capacitance is 100 times the original one, pulsewidth will be 10 times wider. However, when the original capacitors ( 5 x 470 pF ) are removed for 5 x 22nF there isn’t way to generate the laser’s pulse. Do you know what is the reason?
Best Regards
Enrique.
If you consider the Q factor of the circuit you get by increasing 100x the capacitance, that will be < 1 and you’ll get no resonance.
Best solution is to both increase capacitance (by 10x) and add a small air cored RF inductor (start with 10 nH, or about 10x the EPC9150 parasitic inductance).
This is to achieve sinewave drive of the current.
An alternate way for such long pulses is to drive the current with a square waveform, and controlling the duration of the pulse by the ON time of the FET.
In this case, the shunt resistors are used to limit the peak current (by Ohmic voltage drop) and needs to be higher value. The capacitors needs also to be large value because they need to keep the voltage steady for the whole pulse. Finally, usually you need lower supply voltage to start with. Supply voltage defines the dI/dt on the rising edge. I.e. you can look at the EPC9144 board as an example. That was designed for this kind of drive.
Hope this helps