| jesper |
Hi,
How low does the regulator output impedance need to be? I know it’s a tricky question which depends on what you’re feeding, but say I have an op-amp based circuit which class AB outputs. There’s a large amount of op’s so I’d rate the current demand as fairly dynamic.
I’ve been lurking around the internet for a good PSU and the Jung Super regulator is interesting, but right now my gut feeling tells me to look at something simpler without feedback. I’m thinking of a simple series transistor regulator with filtered zener reference followed by a large capacitor bank to lower the output impedance. Before the regulator there is a shottky diode rectifier bridge and a RCRC combination (or maybe LCRC) to filter out line ripple and noise.
The output impedance of the regulator itself is fairly high (some 500mohm) but the output capacitor bank lowers this significantly from some 500hz and up depending on the size of the capacitor bank.
But what about frequencies below 500hz? The PSRR of the op’s is fairly good in this area (min 75dB), but is it good enough.
Does anyone have any real experience?
/Jesper |
|
|
| hjelm |
This is line level opamps?
I guess you can estimate the required supply impedance if you know how much voltage error you can cope with on the output of the opamp. Count backwards with the PSRR of the opamp and you will know how low inpedance you have to have at the given frequency. |
|
|
| jesper |
Hi,
Unfortunately I have lost my simulationfiles for the preamp and active filter, so I can't easily estimate the dynamic current consumption.
But let's do a quick calculation, say each opamp drives 10k, with a worstcase swing of 2V. This gives 200uA of dynamic current for each opamp. There's 12 opamps in each filter, and 4 in the preamp, per channel that is, giving a total of 32 opamp, adding some extra for furter stuff so lets say 40.
Giving a total of 8mA, say 10mA. 1ohm output impedanse gives 10mV of PSU ripple. With 75dB PSRR this translates to about 2uV.
LSB in 16bit data with 2V swing is about 30uV so I guess it's ok.
/Jesper |
|
|
|
