Zener Follower 24 and 48v PSU schematic/layout in here

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Svart

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Joined
Jun 4, 2004
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I threw this together because I needed a power supply for a neve preamp that I'm building.  I have this circuit wired together and working but I haven't tried the layout yet.

All of you home etchers enjoy!

http://www.theopiumdenproductions.com/24_48.pdf
http://www.theopiumdenproductions.com/24_48_layout.pdf
http://www.theopiumdenproductions.com/24_48_place.pdf


Notes on the circuit:  Q1 is the 48v, Q2 is the 24v.  C4 and C5 can be any value that you need.  1uf was just a placeholder.  R2 and R3 can be any load value you need or can be removed.  Those were used for simulation.  R1 and R4 should be exact values for the circuit.  I used 4x 12v zeners to get 48v, you could use any combination you have handy to get 48v, same goes for the 24v zener too.  D6 and D5 were used as voltage drops to get the voltage on the base to "collector+.7v" to get exactly the required voltage out of the emitters.  You can use any silicon diode here.  AC input on my design was an Amveco 2x22 transformer with secondaries wired in series.  You get about 57VDC after rectification (losses are added in the equation).

*Permission is NOT granted for commercial usage of my layout without written permission from me, thanks.*

 
Svart said:
I threw this together because I needed a power supply for a neve preamp that I'm building.  I have this circuit wired together and working but I haven't tried the layout yet.

All of you home etchers enjoy!

http://www.theopiumdenproductions.com/24_48.pdf
http://www.theopiumdenproductions.com/24_48_layout.pdf
http://www.theopiumdenproductions.com/24_48_place.pdf


Notes on the circuit:  Q1 is the 48v, Q2 is the 24v.  C4 and C5 can be any value that you need.  1uf was just a placeholder.  R2 and R3 can be any load value you need or can be removed.  Those were used for simulation.  R1 and R4 should be exact values for the circuit.  I used 4x 12v zeners to get 48v, you could use any combination you have handy to get 48v, same goes for the 24v zener too.  D6 and D5 were used as voltage drops to get the voltage on the base to "collector+.7v" to get exactly the required voltage out of the emitters.  You can use any silicon diode here.  AC input on my design was an Amveco 2x22 transformer with secondaries wired in series.  You get about 57VDC after rectification (losses are added in the equation).

*Permission is NOT granted for commercial usage of my layout without written permission from me, thanks.*
As it is, this circuit is very sensitive to output short-circuit. If a short happens, the Zener capacitor (C1 or C2) discharges in the b-e junction and fries it instantly. You should add a resistor from the zener to the base of the transistor. And I would use somewhat larger caps across the zeners.
 
abbey road d enfer said:
As it is, this circuit is very sensitive to output short-circuit. If a short happens, the Zener capacitor (C1 or C2) discharges in the b-e junction and fries it instantly. You should add a resistor from the zener to the base of the transistor. And I would use somewhat larger caps across the zeners.

At least he's not using 3 terminal adjustable regs.  Well done Svart  :)

Some thoughts if I may:

A small resistance (2 - 5 ohms) after the main diode bridge before the first filter cap will get rid of some diode bridge noise. Largish W or several 1/2W in // would help them not burn up on power on.   

Using several filter caps in // to get your 10,000uF will lower ESR. 

Another bank (mainly on the audio 24V) of 1 ohm or so and another 10,000uF bank would not leave all the ripple reduction to the cap multiplier.

R1 and R2 supply about 5mA to the zeners which is good. They're quietest around there. 

Another 1N4004 from R1/C1 junction to unreg'ed V will help with discharge of C1.  Same with the R4/C2 junction.

A resistor from the top of the zener strings to the bases with another cap from base to ground would get rid of more zener noise.  Use a slowish time constant for voltage ramp up (they'll think it's tubes!) I did one once that used a really nice big poly cap there and had a 4+ minute time constant.  No noise at all!

An active current source (again 5mA) to the zeners instead of resistors R1 and R2 would be another refinement to isolate the reg'ed from unreg'ed.

Isolate the output of the follower with a few ohms (3R?)before the output cap.

Use a differential filter on the secondary of your power transformer to get rid of some mains hash.  Especially if your using a wider bandwidth torroidal.


After saying that, nice to see a better sounding than the usual LM1085 etc. reg circuit   :)


Edit: I also think HexFreds are a good investment over 1N4000 series.  Schottky diodes are quieter too but some are voltage limited, good for tube heaters though. 
 
Looks interesting, thanks for sharing.

On top of abbey's and Winston's remarks:

- if you have a fast enough transistor and low-ESR capacitors on B and E, you may want to include a small base stopper resistor (or ferrite bead, if you're trying to get the very best audio-band noise performance) on Q1 and Q2

- for short circuit (and on/off-transient) protection you may want to include a diode between B and E of Q1/Q2

EDIT: should have mentioned that this is for input short circuit protection and/or transients. A common scenario is that you switch off the mains, +24V keeps drawing current and drags down your unregulated rail while the +48V reservoir cap is still fully charged. At some stage Q1's base-emitter junction gets reverse biased enough to start zenering, and that 1k resistor may or may not be enough of a current limit to protect the transistor. For good measure I'd include a diode between E and C as well.

- the thing isn't very green, is it?  ;)  A power resistor in the collector connection of Q2 sized for ~24V drop at maximum operating current will likely be cheaper than a large heat sink for Q2 (plus it serves as another overload protection measure)

JDB.
 
Thanks for all the information guys.  I primarily drew up the schematic with what I had in my parts bin which is why it's kind of sparse.  I'm also trying to get back to simply playing around with audio electronics again.  I've spent the last couple of years designing RF products that have to work without fail and I've felt at times that I have lost the love of simply playing around and making things catch fire while not being under intense pressure to meet deadlines.

That being said, lets get to the discussions!


A small resistance (2 - 5 ohms) after the main diode bridge before the first filter cap will get rid of some diode bridge noise. Largish W or several 1/2W in // would help them not burn up on power on.

That's interesting.  I've not done any resistance in series with the output of the diode bridge before on any design.  I mainly do RF design and it's a big NO-NO to have series resistance anywhere as your PSU is intended to be as low impedance as possible.  Of course I don't know how this applies to pre-regulation so I'll be happy to try it out. 


Using several filter caps in // to get your 10,000uF will lower ESR.

This is one of those times where I knew better but I just did the layout with what I had laying around.  Maybe I'll do a revised circuit with all of the goodies. 



R1 and R2 supply about 5mA to the zeners which is good. They're quietest around there.

;)

Another 1N4004 from R1/C1 junction to unreg'ed V will help with discharge of C1.  Same with the R4/C2 junction.

Since I've not really explored this type of topology before(I'm usually on a tight schedule and use packaged lin-regs on most designs), is this more of a robustness addition to keep the base-collector/emitter voltage from becoming too large when power is cut? It was my thought that the zeners would pull the cap down fast enough but then again I haven't actually tested it either. 

A resistor from the top of the zener strings to the bases with another cap from base to ground would get rid of more zener noise.  Use a slowish time constant for voltage ramp up (they'll think it's tubes!) I did one once that used a really nice big poly cap there and had a 4+ minute time constant.  No noise at all!

Elegant.  I'm going to wire that up right away!  Looks like I need to do a revised layout with all of the goodies for sure.  I can find a happy resistor value easily enough but a quick simulation isn't telling me much.


An active current source (again 5mA) to the zeners instead of resistors R1 and R2 would be another refinement to isolate the reg'ed from unreg'ed.

In your opinion, how much do you gain by doing something like this for a circuit like this?



Use a differential filter on the secondary of your power transformer to get rid of some mains hash.  Especially if your using a wider bandwidth torroidal.
 

I generally use a filter network on the AC input to the unit.  Would you still suggest using a common mode filter on the secondaries too?


Edit: I also think HexFreds are a good investment over 1N4000 series.  Schottky diodes are quieter too but some are voltage limited, good for tube heaters though.

Although I built mine using what I had laying around, I do also have a number of MUR860 that I usually use for designs I consider more touchy to power supply circuits.  Bcarso also turned me on to the SiC diodes which are really good but pricey.  Each of my Neve modules has R/C filtering too which is why I went a little sloppy on the main regulation.

- if you have a fast enough transistor and low-ESR capacitors on B and E, you may want to include a small base stopper resistor (or ferrite bead, if you're trying to get the very best audio-band noise performance) on Q1 and Q2

I have plenty of ferrites laying around!

- for short circuit (and on/off-transient) protection you may want to include a diode between B and E of Q1/Q2

This would be in addition to WOB's suggestion for one between B and C?

For good measure I'd include a diode between E and C as well.
 

Working with power MOSFETs and IGBTs has taught me to always have a flywheel diode.  The darlingtons that I am using have internal reverse biased diodes for protection so I didn't add any extra.  I guess anybody who built this would need to make sure that they are protected.

- the thing isn't very green, is it?

;D  The good stuff never is!

A power resistor in the collector connection of Q2 sized for ~24V drop at maximum operating current will likely be cheaper than a large heat sink for Q2 (plus it serves as another overload protection measure

Honestly I don't know how much load I'll be applying once everything is finished.  I took a guess but even with fairly large loads I only dissipate a couple of watts.  Once I get everything working at full capacity I'll take a look at doing this.

Thanks again Abbey, WOB and JDB





 
Can you find some of the older books like the mot power supply design books or other vendor PS design books?  They have good circuits with current limiting and other refinements in them like temp stability.
 
Hey Svart,
Sorry for the slow response, it slipped off my radar.

Me: "A small resistance (2 - 5 ohms) after the main diode bridge..."

Svart: "That's interesting.  I've not done any resistance in series with the output of the diode bridge before on any design.  I mainly do RF design and it's a big NO-NO to have series resistance anywhere as your PSU is intended to be as low impedance as possible.  Of course I don't know how this applies to pre-regulation so I'll be happy to try it out."

It'll get rid of some diode noise. Look at the noise on a scope without the series R and then with.  It's a cheap thing to try. 

Low impedance is good but you'll have that at the follower output.  Plus, there's lots of series resistance in a Neve amp voltage rail.  Anyway, I think it's always best if each stage of a design is optimized at source rather than rely on something downstream for correction or compensation.

Me: "Another 1N4004 from R1/C1 junction..."

Svart: "Since I've not really explored this type of topology before(I'm usually on a tight schedule and use packaged lin-regs on most designs), is this more of a robustness addition to keep the base-collector/emitter voltage from becoming too large when power is cut?"


Yes. It's another cheap thing to throw in there. 

Me: "A resistor from the top of the zener strings...blah!...bases...cap from base to ground... noise...blah, blah..."

Svart: "Elegant.  I'm going to wire that up right away!"

Lemme know : > )


Me: "An active current source (again 5mA) to the zeners..."


Svart: "In your opinion, how much do you gain by doing something like this for a circuit like this?"


It depends on what is being powered. But we want to give the audio circuit the best possible shot at delivering the goods yes?
Ideally, we want the supply to only deliver good clean DC current.  We want to isolate the crap on the rail from the audio AC current loop as much as possible.  Constant current sourcing a shunt regulator is probably best for this but anything we do to help a series reg can't hurt.

Svart: "I generally use a filter network on the AC input to the unit.  Would you still suggest using a common mode filter on the secondaries too?"

I stopped putting a filter on the primary because, in the USA, the power is unbalanced. 
I agree, it would be better to filter the AC mains crap before it hits the transformer but, even with balanced power, I might be tempted to put a filter on the secondary too.  Depends what things looked like.

Svart: "Bcarso also turned me on to the SiC diodes which are really good but pricey.  Each of my Neve modules has R/C filtering too which is why I went a little sloppy on the main regulation."

Yep.  All of this I'm saying might not yeild stellar improvements on a Neve?  But small improvements do add up.  I think it's noble to do the best we can by them.  The supply can easily be adapted for other circuits too. 
If you're powering the class "A" Neve stuff then your output transformer primary inductance is pretty decent at filtering and isolating as well.

About the best rectifier diodes are valve ones I think. Damper diodes being the better choice.  I would want my solid state diodes to mimic those in performance. 
 

I still say it's good to see something other than a 3 terminal reg   :)


Cheers.
 
I had a chance to try this design with the Neve preamps.

5mv pk-pk noise

-90db noise floor.

run barely warm with 4 condenser mics on 4 channels.

no hum, no hiss, no noise of any kind. 

I think I need to redo the layout and sell PCBs or something.  I'm in love.


;D

Thanks guys!
 
I think it could be designed better with a shunt transistor,  temp comp zener setup voltage regulator at the base of the pass transistor and current limiting to protect the supply and what ever the supply is powering.

  I would not want to sell something that relies on a A DIYer that might not even know ohms law using a correctly sized fuse.
 
First, this power supply discussion is great!  Please, please, please, do another schematic with all of the “goodies”.
Second, I use 2 HUGE open frame 24V regulated supplies to power most of my projects, and use on board regulators in each piece of gear to lower the voltage to what I need (bipolar 15V and 18V).  Will these circuits will help “clean up” the power from the open frame units?
Thanks!
Bruno2000
 
I would not want to sell something that relies on a A DIYer that might not even know ohms law using a correctly sized fuse.

It happens all the time around here..  ::)

I see your point but sometimes you have to shoot the engineer and get the project moving as they say..   ;D

I just threw the layout and stuff up so that others can experiment and blow stuff up.  That's how we all learned in the beginning.

I'm not sure I would need to do the whole temp compensated current/voltage source.  It seems to regulate pretty well without getting too fancy.  It sure meets my expectations for what it does.  I suppose better protection is in order for a "final version" though.  If you wanted to collaborate on a design I would be up for that too.

bruno2000 said:
First, this power supply discussion is great!  Please, please, please, do another schematic with all of the “goodies”.
Second, I use 2 HUGE open frame 24V regulated supplies to power most of my projects, and use on board regulators in each piece of gear to lower the voltage to what I need (bipolar 15V and 18V).  Will these circuits will help “clean up” the power from the open frame units?
Thanks!
Bruno2000

Are they linear or SMPS?

how dirty are their outputs?  If they are linear then chances are that you will be just fine with some more R/C/L filtering.  Actually even if they are switchers you could probably do fine with R/C/L networks on the outputs.

 
Svart said:
I would not want to sell something that relies on a A DIYer that might not even know ohms law using a correctly sized fuse.

It happens all the time around here..  ::)

I see your point but sometimes you have to shoot the engineer and get the project moving as they say..   ;D

I just threw the layout and stuff up so that others can experiment and blow stuff up.  That's how we all learned in the beginning.

I'm not sure I would need to do the whole temp compensated current/voltage source.  It seems to regulate pretty well without getting too fancy.  It sure meets my expectations for what it does.  I suppose better protection is in order for a "final version" though.  If you wanted to collaborate on a design I would be up for that too.

bruno2000 said:
First, this power supply discussion is great!  Please, please, please, do another schematic with all of the “goodies”.
Second, I use 2 HUGE open frame 24V regulated supplies to power most of my projects, and use on board regulators in each piece of gear to lower the voltage to what I need (bipolar 15V and 18V).  Will these circuits will help “clean up” the power from the open frame units?
Thanks!
Bruno2000

Are they linear or SMPS?

how dirty are their outputs?  If they are linear then chances are that you will be just fine with some more R/C/L filtering.  Actually even if they are switchers you could probably do fine with R/C/L networks on the outputs.


They are linear, and conservatively rated at 24V 20A each.  I bought them years ago, and have been using the 3 lead regs in my gear ever since.  I used to use the 7800-7900 series, but lately have been using the 317-337 regs, but there always seems to be something better out there.
Bruno2000


 
OK, so I revisited the schematic and attempted to hack in a precision reference, like the TL431.  Things became somewhat complicated and I don't think the precision reference buys us much for the complexity it adds.  I like simple.  If simple works then I like simple even more!

As for protection..  I found the voltage drop across the series resistors to be too much, about 1v. The series resistor was 10R and I dropped 1v, you get the picture.

As for active protection, I'm the kind of guy who used resettable fuses and active crowbars for protection in previous designs..  Is that the sort of thing that you would see in an audio device?  It's fast and reliable but you'll have inductive snap and it'll add cost and complexity.

I'm thinking about an elegant way to use a BJT as feedback to turn the system off once it starts to pull down due to a short.

I also have some other things I'm thinking about that might stir some interest in this type of design too!

 
Svart said:
OK, so I revisited the schematic and attempted to hack in a precision reference, like the TL431.  Things became somewhat complicated and I don't think the precision reference buys us much for the complexity it adds.  I like simple.  If simple works then I like simple even more!

As for protection..  I found the voltage drop across the series resistors to be too much, about 1v. The series resistor was 10R and I dropped 1v, you get the picture.

As for active protection, I'm the kind of guy who used resettable fuses and active crowbars for protection in previous designs..  Is that the sort of thing that you would see in an audio device?  It's fast and reliable but you'll have inductive snap and it'll add cost and complexity.

I'm thinking about an elegant way to use a BJT as feedback to turn the system off once it starts to pull down due to a short.

I also have some other things I'm thinking about that might stir some interest in this type of design too!


Can't wait to see the updated schematic.  What were your results with the Mr. O'Boogie's suggestions?
Best,
Bruno2000
 
I wired the parts directly to my power supply without issue.

Some of the suggestions were for protection, which I can't quantify without testing but I can say that the power supplies are still working just fine after a couple power surges from lightning and a couple intentional shorts by me.

As far as the regulation parts additions, I added them but I did not see a difference in the general noise floor of the outputs.  I'm still sitting around -90db with my gain set to roughly 1/4.  I hear no hum and only a light hiss when gain is raised.  I have not looked at the outputs with a scope as I figured that they are good enough for my ears so they must be good enough for the scope.  Another preamp I have had a slight hum that bothered me.  I put the scope on it and found the noise to be roughly 15mv PK-PK.  I figure that this powersupply must be much lower than that if I can't hear it.


I haven't had a chance to re-draw the schematic properly(it's a rat's nest mess that I threw down for sim) or redo the PCB yet.  I haven't forgotten about it!
 
Great!  Thanks so much.  How would you build a negative regulator?  Is there a complimentary part to the TIP141?
Bruno2000
 

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