CCS Voltage Reference

[Kashmire]

I’m trying to get a low-noise 48V reference for my power supply. My concern is power supply noise reduction (PSNR), because that’s where most of my noise is coming from. For this reason, I have chosen to have a constant current shunt regulator. I’ve attached three schematics:

1) normal zener diode – poor PSNR
2) CCS with a voltage-dropping resistor
3) CCS with a voltage-dropping zener

The reference has to deliver less than 1mA. The CCS can be:

- CR470 (~5mA)
- J511 (~5mA)
- LM134/234/334 (5-10mA)
- 1N5314 (~4mA)
- E-452 (~5mA)
- IXCP10M45 (10mA)

I’m inclined to use the IXCP10M4 (or the adjustable version IXCP10M45S), because I already have some, and it reputably has good performance/sound (see Pete Millett's site ). Additionally, the IXCP is worry-free in terms of robustness, thermal considerations, and it even includes a reverse bias protection diode – all good things for the DIY’er.

Question: Which schematic is better – (2) or (3) – for PSNR as the primary concern?

[Kashmire]

FYI - SPICE simulation shows (3) is the best performing, even though SPICE simulations usually don't tell the whole story. However, SPICE predicts performance with amazing accuracy.