LT3080 High Voltage Floating Regulator

In the Power Supply Section of the new edition of "Art of Electronics" a simple HV regulator using Linear Tech's LT3080. This seems to work nicely:


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What if we raise the bar a bit and make it more useable by getting rid of the CCS and instead use resistors and a cascade of mosfets to raise useable current to lets say 200mA and share the HV drop to 2 mosfets? In the simulation seems to be able to handle shorts but c3 puzzles me a bit in case of direct short circuit.


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I've been away in Spain for a few days visiting a supplier, so haven't had much time to investigate.

D1 shouldn't make a difference, and that's how it's shown in Figure 9.113 of the new AofE.

The cap on Iset's resistor isn't necessary at this point, but is discussed over a few paragraphs in the datasheet.
LT3080 version of series regulator

Hello jacjinnj,

Tom in Calgary has gone to the dark side and his series regulator in now commercial. No longer DIY supported.

Looking at your first post in this thread the STP8NM60 in the CCS is obsolete. (Is there a substitute?)

Are you using or building this LT3080 version of series regulator? If so with what results?

Thanks DT
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20dB’s of difference

I don’t have a dog in the hunt other than noise and PSRR are important.

I think that I will build one of each and see how they test. The data sheets do not show 20dB’s of difference.

The thing that irritates me some is that Tom used the open source and network of diyAudio to develop his project. After everyone’s generous help his project is now personal proprietary property.

My apologies to Tom in Calgary, this topic has been well rehearsed:

No worries.

Tom in Calgary has gone to the dark side and his series regulator in now commercial. No longer DIY supported.

Not at all. I fully support DIY. I just don't give my circuits away for free like I used to. Turns out you can't run a business if you give away your product for free. Who'd have thought. :)

As Jack points out I've been using the LT3080 in a Maida-style regulator for years now. It works very well. With low-current zeners you can minimize the input-to-output coupling and get truly stellar line regulation.

I would probably opt for the LT3081 which uses 50uA "set" current.

I haven't found the 10 uA of the LT3080 to be an issue. As long as you're reasonably careful with the layout and clean up the flux after soldering up the board, you'll be fine. It never ceases to amaze me how a little flux in the wrong place will completely blow the performance of a precision DC system.
Obviously with 5x the Iset, you can have 5x the amount of flux contamination. ;)

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Side by Side by Side


To put this into perspective I am making a SET 12B4A headphone amplifier. First the goal is to get the noise floor as quiet as possible for as few dollars as possible. The next step is to tune the 12B4A SET to minimize the FFT harmonic profile. That leads to optimizing the signal to noise Raito at the equivalent output of 90dB into Audeze LCD-2 headphones. (About 1 v RMS into 70ohms)

I have assembled the three different regulators; one of Pete’s, one of Tom’s and a Salas style HV Shunt from K&K Audio.

I will test these with the AP 2522 on the bench.



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Hello DT,

Have you some feedback about your comparison of power supply ?

I have also made two different style of power supply for my RIAA preampli ( Merlin RIAA Preamp ), the first one is a simple version stabilized with three 100 V Zener diodes and the second one use a LT3080 in a Maida like regulator... I wanted to be able to use it also as a high voltage variable lab power supply (50 - 350 V). The un-populated part of the second PCB is just a 6.3 V 5 A regulated power supply for heaters, like in the first version (it is too much for the preampli, but the power supply can also be used with a power amplifier).

It is quite different than the ones you are testing since I wanted to have on the same PCB both the high voltage and the 6.3 V heater power supply and their rectifier with the 100 uF 400 V and the 10'000 uF 25 V capacitors, therefor it can be directly connected to my toroïdal transformer as you can see on the third photo (the heater should be 6.3 V, I have to replace a 470 ohms resistor by a 487 ohms, i didn't have them in stock when I have build the board)...

The connector indicated "SELF" can be used in the filter area of the power supply to connect a resistor (C-R-C) or a choke like in the last photo (C-L-C) or even a NTC to reduce power on surge current, but it can also be simply ignored and connected with a wire !

The first power supply is working very well and is currently powering my RIAA preampli :)

I have started the test with the second one, but I have the following problem : with the input voltage of 250 V AC (about 350 V DC) I can only adjust the output voltage from 47 V (this is OK for the fixed resistor) to 177 V :eek: I am using a fixed 47k resistor and a 470 pot that I can use only on one third of total course !

May be the circuit don't like the 10 inches connection to the pot ?



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Hello Merlin,

Below is the schematic of this power supply.

It is a second version after the one with three 100 V Zener, very similar to the 300 V power supply described in your book Fig. 11.46 but with a current source for the Zener and no current limit. It was shown in the RIAA thread : Merlin RIAA Preamp and as you comment it, this power supply is working very well with the RIAA preampli :)

This second power supply is closer to the Maida regulator in your book Fig. 11.48, but with a LT3080 regulator which offer an improvement of 20 dB PSRR over the venerable LM317. It has been used by several people on this forum (like Tom) with very good results : 21st Century Maida Regulator I am using an IRFI840G for the MOSFET, it is not very powerful (only 43 W...), but I made a mistake on the layout using a MOSFET TO220 pattern instead os a TO247 :mad: It is enough for the preliminary test but later I will adapt a more powerful transistor...



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