Q:

Running high powered/current LEDs with high frequency

firstly i would want to thank all who are willing to help me in this problem that i am facing.
So to begin, i am a high school student doing a final year project. Basically i have to create a circuit where by a 1000Hz frequency is an input that i have to alternate it so that my output will be toggling with half of the input frequency.
Therefore i am using a single J-K Flip Flop which has a Q & Q(bar) output. That i do not have a problem....
However the problem comes in here. from the 2 outputs of my J-K Flip Flop, i have to use each output to power up 20 LEDs in series, which has to be 1.7V each LED and 700mA, making it 34V with 700mA.
But the output of a J-K Flip Flop does not produce enough voltage and current.
i have tried using a BuckPuck after the output, and realise the rise and fall time is too slow for the high frequency.
i found out that a NPN Transistir ( BD137 ) has a very fast Rise and Fall time, however after configuring the circuit, the output measure was 34v But only 200mA....
please help me to get a 34V and 700mA, thank you.

A:

The simple way is to use the signal to turn on a FET:

simulate this circuit – Schematic created using CircuitLab
The FET needs to have a threshold voltage (Vgs) well below the output of the J/K, ideally in the 2-3 V region if it's a 5 V flip flop. You also want the on resistance (Rds on) to be low enough that the power consumption at 700mA isn't an issue (power = I2*R). The maximum on current (Id MAX) should also be well over 700mA. Finally the maximum allowed drain-source voltage must be over 34V. 

