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Design >> Analog Design >> Type of feedback in voltage regulator
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Message started by analog_wiz on Nov 26^th, 2012, 2:42am

Title: Type of feedback in voltage regulator
Post by analog_wiz on Nov 26^th, 2012, 2:42am

Hi, Whats the type of feedback in a standard pmos ldo. I mean, what is sampled at the output is it voltage or current. Also in a current mode bandgap(eg:banba)i believe we are sampling the output current and feeding back voltage(through the diode connected bandgap).I dont see any actual difference between the two (banba bandgap and a pmos ldo standard topo with error amp and output pmos stage). I wanted to know if there is any sure shot method of identifying the sampling.

Title: Re: Type of feedback in voltage regulator
Post by raja.cedt on Nov 26^th, 2012, 2:48am

i don't know abut BGR, but in LDO it is voltage-voltage feedback.

Thanks,
Raj.

Title: Re: Type of feedback in voltage regulator
Post by analog_wiz on Nov 26^th, 2012, 2:58am

Raja, I know that it has to be voltage series( otherwise it would not be used in the first place,psrr would be bad). But when comparing it with a current mode bandgap topology which also looks similar iam not able to understand why it should be shunt sampling in ldo at output and series sampling in a bandgap output. I need some explanation on this.

Title: Re: Type of feedback in voltage regulator
Post by raja.cedt on Nov 26^th, 2012, 3:26am

hello,
i don't about this bgr, if you are talking about fig 2 in this pap http://www.ing.unibs.it/~richelli/matpdsia/bg1.pdf, then it is voltage sampling only. The feedback has to give accurate voltage so i will sample voltage and give it to op amp which adjust pmos gate . Same in LDO also.

Thanks,
Raj.