# Closed loop control of PWM using current sensing method

This is the block diagram of the project i am working on. I have a DC voltage range of input as 8V to 16V. The duty cycle at the PWM generation should change automatically from 10% to 90%. I require 1A current constantly to the load despite change in duty cycle of PWM signal. For this purpose, the current sense and control block is used in feedback where I prefer using shunt resistor method. The driver to drive the load I want to use is a MOSFET. The load let us assume is purely resistive and not inductive.

Please help me know on how should I go forward with it. Which method should I use to generate PWM waveform? What MOSFET should i use such that it withstands a little more than 1A current, and how should I design the resistance value of current sensing resistor?

• do a search for arduino motor driver – jsotola Feb 8 '18 at 6:46
• Welcome to the site. Please quickly realise that this is not a free design house, homework-answering service or an on-line technical encyclopedia, copied out to you on demand. People will help you take the next step if your question shows that you've done as much as you possibly could on your own - which your post doesn't, I'm afraid. Please revise your question showing your work and findings so far, in considerable detail. Or delete the question if Internet searches give you your answer anyway. Again, a warm welcome to the site. – TonyM Feb 8 '18 at 6:56
• Feedback goes before PWM controller, not after. – Gregory Kornblum Aug 27 '18 at 6:20

I require 1A current constantly to the load despite change in duty cycle of PWM signal.

If you need 1 amp constant to the load, why are you trying to control it with PWM? Why not use a 1 amp constant current generator: -

The circuit above works by negative feedback to take enough current through the load to ensure that the voltage across the 1 ohm resistor equals the control voltage. So, if the control voltage is 1 volt, then the current through the load has to be 1 amp because the shunt resistor is 1 ohm. This can be made with smaller values of resistor such as 0.1 ohm but it can start to become trickier.

If you do need to control this with PWM (despite you wanting 1 amp constantly), you can low-pass filter the PWM output to produce the analogue control voltage.

Which method should I use to generate PWM waveform?

Do you need to is my question.

What MOSFET should i use such that it withstands a little more than 1A current

Well, we don't normally respond to direct questions regarding product recommendations but most MOSFETs can handle over 1 amp especially DPAK, D2PAK, T0-220 case sizes etc..