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Analog PI controller with one aop-amp

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gary36

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Can anybody tell me how to implement PI controller circuit with only one op-amp. Many references provide atleast 3 op-amps
 

What is a PI controller ? PID controller w/o the differentiator ? This is PD, could
be converted to PI.

Something like this

Regards, Dana.
 
Last edited:

PI controller is PID without D.

Sure a PI controller (also PID) can be build with a single OP.

1595603218128.png


R1=R2, R3=R4, C1=C2
R3/R1=Kp, C1*R3 = Ti
What are the intended process value, setpoint and manipulated value voltage ranges?
 

What is the value of ki, is it 1/Ti? and kp and ki are not independently adjustable as per your above circuit
 

gary36 said:
What is the value of ki, is it 1/Ti? and kp and ki are not independently adjustable as per your above circuit
Click to expand...
I think, ki is kp/Ti. As you know there are different ways to present PI controller parameters. I feel Ti and Td notation being more descriptive than ki and kd. There's a direct relation to empirical controller tuning methods.

If you rely on the "parallel" kx controller structure and independent adjustment of its parameters, you should use multiple OP.

With a basic understanding of PI(D) transfer functions, you are surely able to derive the relations.
 

Here is an example of a single chip PSOC with PI controller example for a BLDC
motor. Note it does not use OpAmps, but does have 2 OpAmps that can be used
for other tasks. Note right hand window shows many onchip resources were not
used, and available for other tasks. Also this is a low end part, higher end parts
have 20 bit DelSig, DSP Filtering, more analog, like more OpAmps......


1595680248093.png



A short video on a specific kit (your design I think a $ 10 kit would suffice) -



A PI fan control single chip solution here - https://www.cypress.com/file/139661/download

and https://www.cypress.com/documentation/application-notes/an89346-psoc-4-intelligent-fan-controller


Regards, Dana.
 
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The most simple PI-controller is an inverting opamp configuration with an R1-C1 series connection in the fedback path (input resistor Ro).
The transfer function is

H(s)=-Kp(1+sTn)/sTn

with: Kp=R1/Ro and Tn=R1*C1
 
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    d123

    d123

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Hi LvW

Did you mean ki= 1 /Ro *C1 and not 1/R1*C1 and Kp is R1/Ro
 

gary36 said:
Hi LvW
Did you mean ki= 1 /Ro *C1 and not 1/R1*C1 and Kp is R1/Ro
Click to expand...
Hi Gary ,
I don`t know the meaning of your "ki". In my equation there is a time constant Tn which is Tn=R1C1.
 

The ki versus Ti point has been already answered in post #3 and #5.

You should be able to derive the transfer function of the simple OP circuit yourself and relate it to your preferred PI controller description.

@LvW: ki is the "integral gain" in the popular parallel PI controller description
H(s) = -(kp + ki*1/s)
 

FvM said:
...ki is the "integral gain" in the popular parallel PI controller description
H(s) = -(kp + ki*1/s)
Click to expand...

FvM - thank you. I could imagine...
However, I don`t like to see in a question such symbols/abbreviations without explanation.
(Example: What is the ro with Rc=1k and ro´=20k and Ro=1k with B=100)
 
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