Power regulation on a voltage regulator

Jan 17, 2009 2 Replies
S

Hi I have a working programmable voltage regulator, and I want to add a power regulation loop that feeds the voltage regulation vref. I am currently reading in the current and voltage by ADCs.



My idea for the power regulator inputs are: Vmax = the maximum voltage to regulate to (constant) Iadc = the current on the output of the voltage regulator Vadc = the voltage on the output of the voltage regulator P = Iadc * Vadc Pref = the constant desired power output Gain = the constant adjustable gain



I am guessing I cannot simply calculate the voltage like this:



Vreg = (Pref - P) * gain if(Vreg > Vmax) { Vreg = Vmax }



This will not work because power and voltage have different dimensions?



How do you do this?



Scott


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G

Scott : What you suggested will work. The dimensional question is resolved by considering that Gain has a dimension of Watt-Ohms (maybe I got this wrong - but you get the idea) You will get an inevitable steady state error because you have a P-only error driven system. Consider adding an integral term to the Vref quantity. You are also going to have to consider issues of dynamic response and stability in selecting the gains If you know something about the load, you should add feed-forward terms to the Vreg term as well as the P & I terms (for example, if you know that the nominal resistance of the load is R, Vreg_ff = SQRT(Pref*R)

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M

Are your settings constant?

I assume you want to do something like this only without looping and incrementing.

if ((Iout*Vout) < Pmax) and (Vout < Vmax) Increase Vout

if ((Iout * Vout) > Pmax) Decrease Vout

If this is what you want, there is a little more information needed about the nature of the load. If the load is a very large capacitor or a zener diode or the like, it is a much different problem than if it is resistive.

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