Hi,
Since there are many clever people here with much more experience than I, I wanted to get some counseling on how to do this.
I don't want to talk too much about my application (I don't want to explain too much why I'm going for this or that, since this was already carefully thought).
I have to get very short LED flashes pulsed at high speed for specific reasons, so the load is a set of high quality HB LEDs.
I have this schematic, which I'm trying to achieve :
I would like to synchronize Q1 and Q2 to have those state transitions:
ON -> OFF
1. Open Q1
2. Wait 10ns (ideally)
3. Close Q2
OFF -> ON
1. Open Q2
2. Wait 10 ns (ideally)
3. Close Q1
I want to switch the capacitor while it's charged to 36V, so this makes it a bit more challenging as well, because I have to drive the Q1 NMOS gate with a MOSFET driver with e.g. 45V so that when Vload=36V, Vgs = 45-36=9V. Since the MOSFET body diode could conduct when the capacitor is charged at 36V and Vload=0, I have to put the NMOS with the source at Vload node. I don't really have a better solution than a high voltage MOSFET driver IC like the LTC4440 for example, but I do have a 45V source in the circuit so this would work. I also wonder if there would not be a better way to implement Q1 than only one NMOS.
Q2 could very well be a NMOS (same kind as Q1 for example) :
The thing I'm most unsure about is the synchronization of Q1 and Q2. Basically Q1 and Q2 must never conduct at the same time. I wonder if anybody have an idea on how to achieve this synchronization. I *will* have an FPGA on this project, so I *guess* (actually, if you have suggestions for FPGAs I could take them) it could be done with my FPGA, but still, I wonder if I could not make this possible only with ICs/discrete components/logic gates in order to use a single clock! I'm trying to switch as fast as around 200ns, so this is my target.
Are there solutions on the market to synchronize two MOSFETs properly and fast enough? From my requirements, it seems I have to make the opening time faster than the closing time. Indeed, if Q1 and Q2 are the same, and Q1 and Q2 open faster than they close, then my delay requirements would be met. If you guys have ideas on implementing this, or suggestions, feel free to let me know!
Thanks!