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Old 5th September 2003, 03:35 AM   #1
grataku is offline grataku  United States
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Default Hi voltage Jung super reg

Hi,
I have been thinking about super regulating the +/- 70 V of the BOSOZ or some type of X variation thereof...would that be worth it? I have quite a few BB 3584JM high voltage opamp to use in place of the AD825.

The voltage seems to be in an intermediate range that is too high for the std superreg but maybe too low for shunt reg, I don't know.

Anythink wrong with the idea? Or would it be better to redesign the BOSOZ for lower voltage around a small signal mosfet like ones in the ZETEX series?
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Old 5th September 2003, 04:43 AM   #2
andy_c is offline andy_c  United States
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Default Re: Hi voltage Jung super reg

Well, whether or not it's worth it for your application I'm not sure (I don't know what a BOSOZ is). But I've been playing around with sims for a design of a super reg of +/- 90 V at about 100 mA (with 300 mA transients or so) for a class B MOSFET power amp minus the output stage. It's not necessary to use a high-voltage op-amp. The design I have uses a TL431 as a shunt regulator of 30 V for a normal op-amp, with the shunt regulator bias resistor bootstrapped to the 90 V regulated output. One drawback is the bias resistor dissipates about one Watt. I chose the 8-pin DIP version of the TL431 instead of the TO-92 for thermal reasons, as it dissipates about 300 mW. Just choose the zener diode in the output stage so that the op-amp output is biased midway between its rails, about 15V. I use zeners that total about 75 Volts here.
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Old 5th September 2003, 06:32 AM   #3
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Have you thought about the simple LM317? This regulator can regulate rather high voltage if not the voltage across it isn't more than 35 (60) volts. One thing to remember: The feedback network consumes power, rather much, at high voltages.
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Old 5th September 2003, 12:21 PM   #4
grataku is offline grataku  United States
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BOSOZ = Nelson Pass balanced linestage or bride of son of zen.

What I was thinking was to use the ALW/Jung circuit. In the standard circuit the superreg op amp is an AD 825 which is fed by the super regulated output voltage (up to 30V output) the LM317 is already present and functions as a pre regulator.

I looked at the datasheet of the 3485JM again and the PS voltage needed is too high! I guess I misread the oprating voltage. A minimum of 70-0-70 to a max of 150-0-150. At 300 V it looks like I could make a Jung super reg for a tube amp!
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Old 5th September 2003, 01:42 PM   #5
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Hi Grataku,

I've been playing with this a long time ago, and even mailed Walt Jung to have some hints about the HV problem, and he replied quite gently. Normaly, everything should work fine, except that you will have to address a huge dissipation issue, both in the op-amp and in the controlled BJT. I used an OPA445 from BB (now TI), rated for 90V in a 80V supply, and it ran quite hot . The only way - AFAIK - to reduce the dissipation is to lower the current delivered by the op-amp to the base of the BJT. So it requires some trimming, adjusting the CCS current and chosing a high gain BJT. Such power BJTs are not common (high gain doesn't suit to power requirements). I ended up with a power darlington. I had no sufficient Vout-Vin drop in my app to use a power mosfet as pass element, but I still wonder if a Mosfet would give the same overall performances than a BJT...

Just my ...
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Old 5th September 2003, 02:54 PM   #6
andy_c is offline andy_c  United States
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Quote:
Originally posted by peranders
Have you thought about the simple LM317? This regulator can regulate rather high voltage if not the voltage across it isn't more than 35 (60) volts. One thing to remember: The feedback network consumes power, rather much, at high voltages.
With the LM317, how does one solve the problem of having the entire unregulated input voltage appearing across the internal pass element at startup without having a large voltage drop in series with the unregulated input in normal operation?
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Old 5th September 2003, 05:29 PM   #7
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Default use the TL783

this is a 125 volt regulator from Texas Instruments -- just outboard a heftier pass transistor.

you can then go the further mile by using the Wenzel Associates feedback design to get the noise down further -- to that approaching a low noise reference. Seems like a lot of work for a power amp, but that's what we're in business for.

don't forget also that you can always regulate the ground return leg of a single ended power supply.
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Old 5th September 2003, 05:46 PM   #8
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Quote:
Originally posted by andy_c


With the LM317, how does one solve the problem of having the entire unregulated input voltage appearing across the internal pass element at startup without having a large voltage drop in series with the unregulated input in normal operation?
The standard cheating way of using a zener from adjust to ground. The reg tries to maintain the 1.25 V across the resistor from output to adjust so when you put e.g. a 75 zener from adjust to ground then you can handle some 125 V input and regulate between 76.25 and some 120 V.
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Old 5th September 2003, 06:40 PM   #9
andy_c is offline andy_c  United States
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Quote:
Originally posted by UrSv


The standard cheating way of using a zener from adjust to ground. The reg tries to maintain the 1.25 V across the resistor from output to adjust so when you put e.g. a 75 zener from adjust to ground then you can handle some 125 V input and regulate between 76.25 and some 120 V.
The problem I'm referring to is at startup. At this time, the regulated output voltage is zero because the output cap hasn't begun charging up, and the unregulated input is, say, 100 Volts for a 90 Volt regulator. So there's 100 V across the pass element in this condition. Putting a zener from adjust to ground does not affect the differential between the unregulated input and the regulated output in this case.
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Old 5th September 2003, 09:02 PM   #10
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The disadvantage of using a 317 floating at high voltage is that you need a high division ratio in the feedback to set the output. The regulation factor and basically all performance numbers including noise deteriorate with that division factor. The 783 has the same problem (if you want to call it that).

It is something to keep in mind when making a choice between a floating 317 with reduced performance, or a regulator based on a high voltage opamp, which will lose some performance because of the not-so-hot opamp.

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