Pre amp voltage regulators help.

[sakis]

make shure that capacitor of filter in the input is close to regulator in some datashets is requiered a 100n with it if cap is located far away from bridge ....

also capacitors used to be located in parallel with diodes in many audio and or other application ..... makes rectifing faster

but best of all try after the 100n of the output and close to regulator to add a tantalium 10 mfd

this will change also a lot

[Fanuc]

Originally posted by jackinnj
in any case, the adjustable regulators are quieter than the fixed voltage units, much better still if you bypass the adjust pin with an electrolytic

What I liked was that the fixed 7815 etc had better PSRR in the 1-3Mhz region than most adj. reg's. In fact they may even have better PSRR than Walt Jung's super reg in this region without the boost of a pre reg.

7815 etcs are used in a lot of digital designs remember.

[lumanauw]

Hi, Fanuc,

The 7815 datasheet only shows ripple rejection graph until 100khz. Where you got the data for 1-3mhz from?

[Fanuc]

Originally posted by lumanauw
Hi, Fanuc,

The 7815 datasheet only shows ripple rejection graph until 100khz. Where you got the data for 1-3mhz from?

Walt Jung.

Actually his super reg's (negating the AD797 which has probs with digital/RFi due to undegenerated inputs) have enormous loop gain at LF with a subsequent trade off at HF. This is why the venerable 7815 type design's score and are better than expected at HF.

[Fanuc]

Actually I don't know if a super regulator say with a jfet input like the ad8610 _without the pre reg_ (as this is unfair comparison) could beat a 7815, 7805 at psrr in the Mhz+ region.

Maybe Jan Didden could help us out on that. But i think there definately better than adjustables Lm317 types.

[lumanauw]

Hi, Fanuc,

From LM7815 datasheet, it show at 100khz it has only 35db ripple rejection. I don't know the data for 1-3mhz, but I think it should be lower than 35db. Is this good enough?

[Fanuc]

Originally posted by lumanauw
Hi, Fanuc,

From LM7815 datasheet, it show at 100khz it has only 35db ripple rejection. I don't know the data for 1-3mhz, but I think it should be lower than 35db. Is this good enough?

Have you got any PSRR spec's for adjustables over >1mhz ?

[lumanauw]

Hi, Fanuc,

The values for LM317 at 100khz = 25dB-40dB (depending on Cadj).

For LM2940 at 100khz it's 65dB (but the curve is strange, at 1Mhz it becomes 70dB)

LM2940 is non-adjustable, maybe is this what you mean by comparison of adjustable and non-adjustable (where non-adjustable is better)?

[lumanauw]

The negative regulators are worse. 7915 don't have ripple rejection graph on its datasheet. LM2990 shows only have 20dB at 100khz.

[Fanuc]

Originally posted by lumanauw
Hi, Fanuc,

The values for LM317 at 100khz = 25dB-40dB (depending on Cadj).

For LM2940 at 100khz it's 65dB (but the curve is strange, at 1Mhz it becomes 70dB)

LM2940 is non-adjustable, maybe is this what you mean by comparison of adjustable and non-adjustable (where non-adjustable is better)?

Actually that is pretty damn good PSRR at 1mhz. ! (better than I thought) Will look closer at those devices in digital circuits etc.

Kevin