I want to create 3A pulses that are 5-10 ns long during development. The final pulse width will likely be 7 ns. This is to drive a laser diode with a forward drop of about 4.3V at 3A.
I ordered an EPC9144 to tinker with this notion. I hope that is the right board. This board does not have a complete current sense function.
I think I need to adjust Vbus up until I get the current I want at the pulse width I’m examining. However, I don’t know how to estimate the current. The example 'scope illustration for the board shows a current pulse of 8.3A, but it is unclear to me how that is estimated from the 'scope traces. Do I get that from Vds? The drop in charge capacitor voltage and the pulse width? Differential across the laser diode?
EPC9144 should work for you, but current measurement is very difficult at those pulse widths: that’s why we did not include the circuit.
If you need higher voltage you can also look at the EPC9154 – 40 V, 10 A High Current Pulsed Laser Diode Driver (epc-co.com)
Is it possible for you to measure the optical power on the output?
As an alternative you could measure the average power input and calculate the peak depending on your repetition rate and shape of the pulse.
I hope this helps…
Thank you for your quick response, Andrea!
Alas, I don’t have tools in this location to measure the output pulse energy. That would have been a nice unobtrusive way to do this.
I like measuring the average power in. With 3A - 10ns pulses at 200 pulses per second, the current is 6 uA. I can insert a 100K high-side shunt and put the bench meter on that. I imagine I can get the pulse width from the drain voltage sense. I am not sure how to estimate the shape of the actual current pulse. Should that be pretty square for 5 ns to 10 ns?
As you can imagine, I don’t want to break my laser diode.
For the pulse shape, you can get some idea from measurement, but maybe some simulations can help to. Are you aiming for a square wave?
I guess I’m hoping for a 2 ns rise time, 3 ns top and 6 ns fall time. However, I’m fine with 1 ns rise time, 6 ns top and 2 ns fall time. Or (if need be) a triangle with 6 ns rise and 7 ns fall. (By rise time, I mean the start of the current pulse.)
I’m not sure how to infer the shape from the drain waveform.
rise and fall times can be deducted from the drain waveform, but for the shape I would recommend using a SPice simulation to give you an idea of the shape.
I will go with the rise and fall times for now. Once things kinda work, I will think about simulation.
I finally got to using the board. I set the current using the average current (knowing the duty cycle and guessing at the rise and fall times). I elected to remove the 50-ohm resistors from the board to make the estimation much easier.