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wrenchone 29th November 2010 10:35 PM

Crazy Current Mode Shunt Regulator
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I'm dropping this circuit in the analogue source forum, as it would most likely be used on an RIAA preamp. This ciruit is somewhat similar in priciple to the Salas simplistic shunt regulator, but adds a common base stage and Darlington to act as error amplifier/current comparator, and uses a resistor rather than a zener to determine output voltage, along with a jfet reference current sink. It would be interesting to sub a zener diode (like Salas) for the resistor. This may make it possible to eliminate a stage. I'll try that when I get a little mode idle time. At any rate, this is thrown out as food for thought, and may possibly spur more ideas and spin-offs.

wrenchone 29th November 2010 10:40 PM

1 Attachment(s)
Here's the simulation results for a 0.1A current transient with 10us edges. If you do the math, the dynamic impedance is 4.5 milliohms, and the static impedance is ~0.8 milliohms. A lot of this is due to the second Darlington in the schematic. It would be an interesting experience to build this up and check stability, as only lead compensation is used. The lag capacitor has been reduced to a vanishingly small value (less than what stray capacitance would be), and serves merely as a place holder.

Salas 30th November 2010 05:46 AM

I use resistor or LEDS in many versions too. Would be interesting to check stability in a practical build with all this current gain. Nice project.

wrenchone 30th November 2010 05:51 AM

I've got a zener-based regulator (detailed in one of my other threads) in the RIAA preamp I have installed in my living room system, and I'm thinking of subbing a series string of (15) yellow-green GaP LEDs to see it there's any audible effect. I have the little board all built up and ready to go.

Salas 30th November 2010 06:01 AM

They will need a bypass capacitor too although better for noise.

wrenchone 30th November 2010 06:18 PM

One of ths things I had to check was to see if a large cap across the zener/LED array would have an adverse effect on stability. PSpice says it's all right. Since the cap I chose 180uF, 46 milliohms has a zero a ~17kHz, I guess this is not too surprising. Onward and upward...

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