Linear Regulators

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Hello,

For a pre-amp I am designing, I will be needing a few rails.
Below is a list, and how I thought of achieving them.
All are fed through a 2x18Vac supply (probably Hammond 182L18), rectified with MUR860, bypassed by some small 100nF capacitor.

- 12V for input signal relays (LM7812)
- 5V for the digital circuity (microcontroller, LCD. Microcontroller will achieve its 3.3v using an LDO) (LM7805)
- +/-5/12/15V (TBD) - Analog PSU. Here I thought about using LM317 as from what I understood it yields better performance which might be noticeable
- +/-15V VU Meter driver circuit - LM7815

Would this topology do the job?
What would be the best suggested method for providing this many rails?
(Going with only LM317/LM337's make the PCB quite large so I'm trying to avoid that).
Note that this pre-amplifier do not provide a gain stage, this will be done via a tube part with its own PSU.
Volume control is achieved using a DS1666 IC.

Many thanks
 
Shalom, I've been under the impression that one could get a more precise and less noiseless voltage out of the adjustable regulators compared to the fixed ones. This information should be available in the datasheets or application notes.

The most important design constraint is the required current with each of the supply voltages. These ubiquitous mentioned regulators commonly allow maximum of 1.5 amps output current, but I wouldn't dare take that much out of them. At least the performation (stability, noise issues) might be compromised.

I see nothing inherently wrong with the use of these regulators, maybe someone else has different opinions?
 
Shalom :)

What you said about noise levels is correct - but does it really matter for relay/digital (uC) supplies?

About current requirements - ~500mA on each rail is probably all I'm going to need, unless there are current requirements for an opamp buffer (for the vu meters) I am unaware of
 
eranrund said:
Shalom :)

What you said about noise levels is correct - but does it really matter for relay/digital (uC) supplies?


I think you can have a bit more noisy supply for relay, but not for sensitive digital devices! Personally I would try filter the digital supplies well, and pay attention to the PCB layout as well. That means, a separate ground for analog and digital is recommended.
 
Tube PSU is on a different board, being fed from its own power transformer.
The digital circuity is for volume control (through DS1666), infra-red remote control and input selection (hence the relays - used to choose from several input sources).

About noise reaching digital devices - Except the DS1666 which is fed with its own +/-5v rail, the other devices are not very sensitive and some supply bypass capacitors are all they need.
 
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