The simplistic Salas low voltage shunt regulator - Page 413 - diyAudio
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Old 8th August 2011, 03:11 PM   #4121
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I'm pretty sure that he used a 100 ohm resistor with a 100uF cap in parallel.

For one of my load tests I used an IRFP240 biased into class A with the AP driving the gate. (I think this is the Dieckman circuit). I also have a Jensen transformer which will take about 300mA DC before it distorts -- same one that AP shows in their PSRR test setup. Last is the WJ circuit. It's probably a good idea to compare all 3 for a reality check.

This is straying from the topic a bit, I recognize.
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Old 8th August 2011, 03:20 PM   #4122
iko is offline iko  Canada
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I think it is on topic. It's important to know how we can measure these regulators, after we build them and have such high expectations, performance wise.

I did the same with a power mosfet in class A as load. I measured the RMS voltage and current with a Fluke 8050A. I suppose I could also use a power precision resistor and measure the voltage across it with my Fluke 8920A.
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Old 8th August 2011, 06:54 PM   #4123
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I can measure 10uV DC to 1MHz, if you can send me a built one. ;D

I expect a 4-wire connection would be mandatory.

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Old 8th August 2011, 07:24 PM   #4124
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Quote:
Originally Posted by keantoken View Post
I can measure 10uV DC to 1MHz, if you can send me a built one. ;D

I expect a 4-wire connection would be mandatory.

- keantoken
Maybe you mean 10 uV AC! Well, my 60dB low noise preamp helps me measure below 1uV AC. But we're talking about output impedance here. I haven't measured yet an output impedance so low on any of these regulators.
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Old 8th August 2011, 07:41 PM   #4125
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Nope, 10uV DC, on the scope. So if I test the regulator with a load of 10mA, I can measure an impedance of 1mR. 100mA, 100uR. I can measure this up to 1MHz. Maybe still could with my voltmeter, but I think it only has a BW of 50KHz (or maybe 500KHz, I don't remember).

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Old 9th August 2011, 01:41 PM   #4126
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Hi guys,

rebuilt another shunt reg (since the other guys are performing their duties in my phono stage) and measured again. This time I put 100uF caps across the LEDs for the current source and the norton ref for the voltage regulator.

First, the setup: I use a MOSFET biased in class A, with a source resistor of 1Ohm and an opamp to compare a DC voltage (coming from a 10 turn pot) to set the DC current, plus an AC voltage to overlay the AC current. This has a capacitor and source follower to couple the AC signal on the load input to a BNC socket.
THen, a soundcard (24bit, 192kHz) to look at the spectrum of that signal. I can reliably measure down to about -90dBu with this setup, not limited by the soundcard but limited by the noise in our lab and the whole construction. This is about 0.23uV.
(It actually works a little better, but there is a lot of 50Hz noise and its harmonics, plus some noise, so I want to be on the safe side). Sorry, no schematic, I have a hand-drawn, smeared piece of paper, this load is built from scrap box parts (maybe one day I'll find some time to properly document....)

Starting up the regulator with 16Vin, 12Vout, CCS set to 200mA, load current 100mA, the first positive surprise is that it is not adding any noise. I can't tell if it adds any noise because with my setup I couldnt detect it.

Then, I put a AC current of 27mA @ 1kHz on top, and the output spectrum showed a noise peak of -60dB == 0.8mV. Math gives 28mOhm. Some more work to do, more later.....
(BTW, shorting the diode in the emitter of the PNP yields 3dB improvement...)
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Old 9th August 2011, 01:56 PM   #4127
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Have you measured the AC current of 27mA while driving the regulator with it?
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Old 9th August 2011, 02:15 PM   #4128
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I hate to ask, but where is the schematic for this version? I seem to remember the Salas regs having much lower impedance in simulation.

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Old 9th August 2011, 02:47 PM   #4129
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Come on... simulation... reality... do you remember early on, when I was simulating lots of variations, how I got some crazy output impedance results, past 100kHz? I'd like to see one regulator that could do that in reality. At some point I thought mine could... but until I see it measured independently by a few people with similar results, I'll hold my breath. It looks good on paper though...
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Old 9th August 2011, 03:05 PM   #4130
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Quote:
Originally Posted by keantoken View Post
I hate to ask, but where is the schematic for this version? I seem to remember the Salas regs having much lower impedance in simulation.

- keantoken
There may be a difference between simulation and actual measurements.
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