X-Ray tube Current Control based on PWM

Hi all,

I want a control module to be implemented in FPGA(Altera Cyclone IV 
running on NIOS2) using VHDL which controls current flow to a X-Ray 
tube.

The scenario is I have the expected current value say 5mA. The current 
has to be controlled to 5mA based on the PWM duty cycle %.

Also, based on the current and expected current values I want to find 
the PWM duty cycle required to control the current flow at 5mA to the 
X-Ray tube.

Note: PWM duty cycle is limited to 50% (max).PWM Freq : 150MHz
The current value 5mA is the expected current value and it is given as a 
reference to the control module. At varying PWM% the actual current is 
compared with the expected current. The current flow increases 
supposedly with increasing PWM %. The objective of the controller is to 
find the PWM % at which the current flow is 5mA so that it can be 
controlled.

I hope, I have provided enough information.Since I am a beginner with 
less knowledge in control theory I need some information on how to 
approach this.


Looking forward to your suggestions.

Thankyou!