d123
Advanced Member level 5
[moved] Linear regulator error amplifier input & output voltages & compensation type?
Hi,
The questions are for learning purposes, mainly. I have been reading about both points, and read some related threads here, but haven't found answers yet. I'm having difficulty understanding something and it's beginning to annoy me.
Regarding linear (LDO or Standard) regulators and the error amplifier:
As the error amplifier - which seems to be a difference amplifier - always appears to be balancing the reference voltage to a scaled down output voltage: 1.2 or 2.5, etc. volts...
a) Does the input difference tend to be in the range of a few millivolts?
b) If so, how is the error amplifier output voltage scaled to the driver transistor or directly to the pass device? How much gain is appropriate for a design made with individual ICs? Is there some "normal" limit to line regulation that can be predicted? Is the output off set to match the transistor base emitter/MOSFET turn on to saturation voltage?
Trying to find the above info., I found info. about compensation types 1, 2 and 3, so I'm only just beginning to understand what poles and zeroes are in this respect...
2) Do any and all linear (not switching) regulator error amplifiers need some type of compensation to avoid oscillation? If so, for a non-engineer, how could I assess a circuits needs?
If questions like this, without needing to refer to a specific design, are able to be answered in general, overview way, great.
Thanks
Hi,
The questions are for learning purposes, mainly. I have been reading about both points, and read some related threads here, but haven't found answers yet. I'm having difficulty understanding something and it's beginning to annoy me.
Regarding linear (LDO or Standard) regulators and the error amplifier:
As the error amplifier - which seems to be a difference amplifier - always appears to be balancing the reference voltage to a scaled down output voltage: 1.2 or 2.5, etc. volts...
a) Does the input difference tend to be in the range of a few millivolts?
b) If so, how is the error amplifier output voltage scaled to the driver transistor or directly to the pass device? How much gain is appropriate for a design made with individual ICs? Is there some "normal" limit to line regulation that can be predicted? Is the output off set to match the transistor base emitter/MOSFET turn on to saturation voltage?
Trying to find the above info., I found info. about compensation types 1, 2 and 3, so I'm only just beginning to understand what poles and zeroes are in this respect...
2) Do any and all linear (not switching) regulator error amplifiers need some type of compensation to avoid oscillation? If so, for a non-engineer, how could I assess a circuits needs?
If questions like this, without needing to refer to a specific design, are able to be answered in general, overview way, great.
Thanks