or use an opamp + a buffer.
A simple opamp buffer would consistent of an opamp, 1 base resistor (optional) and an output device (npn or n-channel) rated for this. Connect the opamp's output to the npn's base through the base resistor. npn's collector to your power source. npn's emitter to the load and the opamp's inverting input. opamp's non-inverting input to your pwm output signal.