My PWM generator has an offset error which gives my whole circuit an error above the allowed 0,1% of full scale which is 5V. The allowed error is 5 mV.
This error is noticed when i graph my input and output and use the least method sqaure on it.
I need a full PWM from 0% -100%, 0-5V.
These are my values of my error amp: R1 = 30K R2 = 30K
R3 = 33k R4 = 30K
Before i used the above value for R3, it was also 30K and used the underneath formula to calculate my offset with Vref 2,5V i get:
Vo= (1+ (R4/R3)) (R2/(R1+R2))Vref = 2.5V
When i calculate it witg R3 33K i get :
Vo= (1+ (R4/R3)) (R2/(R1+R2))Vref = 2.2V
My problem now is that when i use R3 = 33K for more "current or voltage sensing" my circuit is able to PWM from 0-100%, but with an error above 0.1% of full scale.
When i use R3 = 30K my circuit is not able to PWM from 0-100% in the range from 0V-5V. It than only needs around 0,5V to go from 0% dutycycle to 50% en 0,5V to 100%. in total it only needs 1V to go from 0% to 100%.
i tried to research the error amp, read numerous pdf's but i didn't get any wiser on how to solve this.
I will reiterate my question.
What do i need to change in order to have a full PWM from 0-100%, 0-5V, with an error thats is below 0,1% of fullscale (5mV)?
My professor gave me a hint that i needed to something special with Vref.
Do i need to change something about Vref or something else ? I hope i am clear in my explanation and question. I've been at it for a while, i hope someone can give me the solution!!!
Thanks in advance.
additional info. i cant have two or more links I removed the orginal schematic for my own so you can see what i have done. if you want to see the original, you can find it as an pdf called slau508. My use of PWM generator is slighly different than the slau508.
My schematic and its values, hope you can see it. I forgot to give additional information because i was focusing on the error amplifier