I have used this particular JFET taking advantage of 2 things. 1: It's one of the few that can can have lower pinch off voltage than a BJT's VBE. It actually fills the Jung's criteria for double pinch off there too. 2: Many left overs would be available after the matching process for those who made my NJFET open loop simplistic phono. And that simplistic shunt was developed for that phono. As a partner.
janneman said:
Yes. For Vds=0.5V a 2SK170 is most likely in the saturation region (where it acts as a CCS). Incipient saturation is defined as the region where Vds>Vp 2SK170 has Vp=-0.2...-1.5V so Vds=0.5V will do.
It is unclear to me though what would be the advantage of this regulator. The loop gain looks pretty small (essentially gm(Q3)*R6~40dB, because the ratio between the dynamic impedances of the zener and the JFET CCS is almost 1) so the line regulation and output impedance are not very good.
Its not great. I am no engineer. I just test my DIY ideas. A shunt reg can be surely done technically better.
My criteria, was: Simple, no loop feedback, JFETS and Mosfets, much better sound than battery or LM317.
I did it and met my criteria. Then it has been implemented along my phono by so many people that report it dead silent and great sounding so its ok in my book.
My criteria, was: Simple, no loop feedback, JFETS and Mosfets, much better sound than battery or LM317.
I did it and met my criteria. Then it has been implemented along my phono by so many people that report it dead silent and great sounding so its ok in my book.
salas said:
Well, I got some bad news for you
It has negative feedback, and about 40dB! The negative feedback loop is defined by the dynamic impedance of the zener and the impedance of the JFET CCS. The ratio is very small, so the loop gain is essentially the gain of the base amp (Q3) and the whole thing works as a unity gain amp, or Vo~Vz.BTW, I am sure it sounds great
janneman said:
Of course, another JFET instead of R6 will likely work much better. It will be at Vds = Vgs(on) Q4 which should be fine (it's a few volts). A nice simulation exercise, unfortunately I'm pretty tied right now... Loop stability should also be checked, unity CL gain with high OL gain things can get tricky...
Bonsai said:
First, let me thank you for the stimulating conversation.
I think the entire power system needs to be addressed when looking at these regulators. For example, in the project I am working on today, there is a Jung-type regulator, but there is also an array of 8 39µF OS-CON caps, 8 1µF ceramic caps, and an 800pF capacitance due to the ground planes of the PCB. Output impedance of the whole system is < 100mΩ out to 80MHz and < 1Ω out to 400MHz, which I think is acceptable considering the passband only extends to 96kHz.
Regarding your comment, I agree the ringing was excessive in the plot I posted. It turns out that the AD825 has far better transient behavior than the AD820 (in simulation). I use the AD820 for low voltage outputs since it can swing rail-to-rail and run from a single 5V supply, and I use the AD825 for outputs ≥ 9V.
As you can see from this plot, the transient load response is rather good. For a (quite improbable) 25mA load step with a 10µs rise time, the output swings only about 10µV. That's -68dB @ 100kHz.
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