Running high powered/current LEDs with high frequency
The simple way is to use the signal to turn on a FET:







simulate this circuit &ndash; 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.