analog_sa said:
Ok, so you're using the chokes. Are the 40 uF following the chokes not interfering with the operation?
Well, 40 uf is a pretty small amount considering many series designs use thousands of uf following the control element. But fast transient response of the regulator wasn't one of my primary design goals since all the circuitry it feeds is very stable.
A common improvement (at least technically) of a shunt reg is to feed it from a constant current source instead of a resistor. My experience with this is ambivalent; i guess the CCS design makes or brakes this idea.
Yeah, the key word there is "technically". In high end audio we only care about best sound, and that usually is a result of tampering with the signal as little as possible. There's a lot of potential merit to a design with only copper between the rectifier bridge and the load
jackinnj said:
I would suggest deocupling the lithium battery from the opamp input with a 470R or 1K resistor, perhaps even filtering the battery as reference. I know that NiCads are noisier than alkalines -- I haven't done any testing of Lithium batteries, however.
I haven't really looked into the chemistry of all the different batteries, but lithium cells have a very low self discharge rate, with shelf life specified in decades as opposed to the weeks and months of some types. So from that standpoint, they couldn't really have any noise as that would imply energy dissipation, and in this circuit they are used almost as if they're still on the shelf since the input curent for the AD711 is in the low picoamp range, worst case. I am curious though about your noise measurements since I haven't seen that info before. Are you talking about batteries under load? I agree that batteries aren't ideal low noise power sources and usually benefit from some decoupling and filtering when used to supply current to a low noise circuit. But not in this case when used as a low impedance reference. At least not IME in this circuit, or in the discrete versions I made with mosfets.
Interesting comments. Thanks.