PID design xith 1 operationnal amplifier

S

Thread Starter

S. R.

Hello !

I have to correct a current-regulation loop for battery charger.

I'd like to know if it's possible to create a PID controller with only 1 op-amp.

If someone has an idea, or knows where to find schematics...

Thanks in advance

S.R.
 
> I have to correct a current-regulation loop for battery charger.
>
> I'd like to know if it's possible to create a PID controller with only 1 op-amp.
>
> If someone has an idea, or knows where to find schematics...<

Analog controllers have only one operational amplifier when reduced to their simplest expression: I mean PID controller.

 
Z

Zan Von Flue

hi
I found a schematic from a electronic book I have. The text is in german but the plan and calculations are readable.
The second op-amp is to invert the signal. A transistor maybe enough.

 
M
Use an op amp with an extremely high input impedance. The feed in should be a resistor in parallel with a cap. The feedback should be a resistor in series with a cap. TI is the sum of the two time constants. TD is the parallel combination of the two time constants. If you make the feed in cap twice as big as the feedback cap then you get significantly better overshoot
performance. Yes- this implies that the feedin is the integrator even though this goes against common thinking.

You'll have to work out the variable Prop term and virtual earth maintain on your own.

Cheers,
Mitch
 
J

Johan Bengtsson

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From: [email protected]
To: [email protected]
Subject: RE: APPS: PID design xith 1 operationnal amplifier

Before I start to think about if it is possible or not, I would like to know if you really need the D part of the controller or if PI would be enough.

It also heavily depends on how your input varies and how you want your output to vary.

* Do you have a voltage input and a voltage setpoint and they should be the same, or do you have the control error availiable compared to ground?
* Do you want the output to go up or down when the input goes up?

I would also like to know why you are limited to one OP, could you not just throw in a quad op or whatever you need on a small separate card.

I think the task is quite difficult, that don't mean there isn't a solution, just that it probably sin't worth the job, a quad OP don't cost that much really.


/Johan Bengtsson

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P&L, Innovation in training
Box 252, S-281 23 H{ssleholm SWEDEN
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M
Quad amps won't have the input impedance needed to keep down the steady state droop.

Unless you know of a real good one.

As for the D term - it is critical for temperature control. The gentleman didn't tell us the application.

Mitch
 
J

Johan Bengtsson

Would a LMC660 do? input resistance >1Tohm, sounds quite high at least

besides, I think it would be realtively easy to make it work even for lower input impedance opamps. I have to think more about that however...

I know D term is good for some applications, for temperature control it would be needed in quite a lot of the applications but this was a battery charger and I don't think you really would need the D term there.


/Johan Bengtsson

----------------------------------------
P&L, Innovation in training
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]
Internet: http://www.pol.se/
----------------------------------------
 
M
You will also need extremely low leakage capacitors such as the mylar ones.

Derivative probably won't be needed for a battery charger. It is extremely useful for temperature control provided there are no moving fluids like air or water involved. Never use D if there is a motor involved.

Mitch
 
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