Feedforward - what's this and are there any References?

[CAMALEAO]

Hi everyone,

I would like to know if someone can point me to a good reference explaining what's feedforward, where it is used and why. In addition benefits and cons.

Best regards.

 

[mtwieg]

The wikipedia article is a good place to start: https://en.wikipedia.org/wiki/Feed_forward_(control)

In the context of power supplies, feedforward is when disturbances not associated with the load (Vout and Iout) are fed to the controller. Input voltage is the most common example. If done correctly, it can greatly reduce the effect of supply voltage transients on the load.

 

[CAMALEAO]

Hi, I have but it does not applies for what I want, multistage amplidiers.

 

[FvM]

Feedforward can be both, an unwanted effect and a technique to trim an amplifier frequency characteristic, e.g. feedforward compensation bypassing amplifier stages.

 

[asdf44]

Feedback loops respond to error. I.E. the cruise control of your car only increases the throttle after the car has already slowed down.

A well designed feedforward implementation anticipates what the feedback loop is going to need to do before the error exists to tell the feedback loop it needs to do it. So for example a cruise control system could detect a a hill and preemptively apply additional throttle before the car even had time to slow down. This implementation could greatly improve the response of the system to abrupt changes in road slope.

Feedforward can work well in cases with predictable systems with known relationships that can be 'fed forward' like the one between slope and throttle in the example above.

I personally implemented a feedfoard to anticipate output filter loading on an amplifier and the result was greatly improved waveform quality (particularly because the zero crossing required a large step in the modulator signal)

 

[CAMALEAO]

Thank you very much for your replies guys. I got the idea.

So, thinking the case of an amplifier, I tried to find a simple case where this was being applied but unfortunately didn't find.

Does any of you know about a simple circuit that could demonstrate this?

Like FvM mentioned, we can have undesired effects, and the one that I can think of is the miller compensation, but that's a bad example to demonstrate this.

So do you know any example demonstrating this technique in a simple way?

 

[FvM]

I would look for OPs that optionally use feedforward compensation and study their structure and circuit operation e.g. LM301 or LM318.