# 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 Feb 8 '18 at 6:46
• Feedback goes before PWM controller, not after.
– user76844
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..

• Would that not cause the transistor to operate in its linear region, therefore causing it to dissipate a lot of heat? Apr 3 '20 at 10:46
• @NicolasSchurando yes it would but without going into the world of switch mode constant current generators, you have to live with the dissipation. BTW, for a MOSFET, the linear region is when it is operating as a switch. For a MOSFET (as shown above) it will operate in the saturation region. See this Apr 3 '20 at 10:51