SMPS feedback compensation error amplifier with finite gain at DC?

[waveboy]

Hi,
You have type 1, 2 & 3 error amps for SMPS feedback compensation...
But what is the error amp called that is just a high gain inverting amp?...ie, not an integrating error amp.

Also, can you confirm, that using this (unknown name) error amplifer, there is no gaurantee in eg a Buck battery charger that you would reduce the chances of instability, by using it, instead of a type 1, 2 or 3 error amp?

 

[Compositepro]

It sounds like you are referring to pid (proportional, integral, derivative) control. Without the integral and derivative functions, it is simply called proportional control.

 

[IRstuff]

You seem to be mixing terminology. An error amp is an error amp; the typing (1,2,3) refers to the frequency compensation to provide stabilization and noise immunity for the error amp

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[waveboy]

Thanks, what applications usually get a type 2b error amp in smps?....type 2b is just R and C in pllel in feedback of opamp

 

[IRstuff]

You use the appropriate tool for the appropriate job. You're basically asking whether you should be using a hammer when you can't, or won't, tell me if you're holding a nail or a screw.

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[waveboy]

Thanks, and as you know, there is a type 1 error amplifier, and a type 2b....type 2b is a type 1 but with a resistor connected in pllel to the capacitor.
As you know, the resistor in this place reduces gain at DC......and usually, the power stage poles and zeros in an SMPS mean that the last thing you ever want to do is sacrifice gain at DC.......so why have a type 2b error amplifier which cuts down your gain at DC?....there must be very niche, specific applications for it.......it would need to be an SMPS application which involves a power stage with a very low frequency zero....but what SMPS topology has such a thing?, that a type 2b error amp is needed?

Is it a battery charger?...because the battery is basically a very big capacitor, and the ESR zero is therefore at a very low frequency?...but then again, i thought that the current regulation of battery chargers, basically cancels out the big battery capacitance?

There must be a good reason why people take a type 1 error amplifier, and then add a resistor in parallel to the capacitor?...i cant think of any SMPS power stage that would need such compensation?
...***...
In relation to this, please see bottom pf page 8 of this..

https://www.microsemi.com/document-...tage-mode-current-mode-and-hysteretic-control

"Unfortunately, DC gain does tend to fall at high load currents"

..this epitomises what i mean...high DC gain is desirable in most SMPS's....so why ever drop DC gain by using a type 2b error amplifier?

 

[waveboy]

Also, please could you assist in finding the gain and phase margin of the attached 1kW buck battery charger...PDF schem and LTspice sim attached. The U2 based error amp kind of rules the roost...setting the reference for the U9 based error amp.

 

[waveboy]

Here is the PDF schem, i coudlnt upload it in the same post

 

[IRstuff]

Seems like that's something you can do in a circuit simulator

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