Alcaid said:
1. Good idea.
2. Good idea, but consider power darlingtons too.
3. Fine.
4. Not clear why you need them, but they are backward.
5. No need, this just wastes power and increases hum.
My friend, use a resistor rated for twice the expected dissipation, or 1 watt in this case (round up).
janneman said:
If you are concerned about the output cap discharging into the pass transistors, put a 1n4001 diode in anti-parallel with the pass element (that is, with the + cathode on the input side for the poisitive regulator, and vice versa for the negative). This is highly recommended for 3 terminal regulators also.
Alcaid, you are making this very simple circuit much too difficult, keep it simple. When in doubt, take it out.
janneman said:
Nothing esoteric. Zener noise filtering, level shifting, and the constraint of having to put everything on a couple of mm^2. And yes
Jocko, raw supply rejection is taken care of elsewhere, so I couldn't
care less about the zener impedance deterioration.
slowhands said:
This is not a 3-terminal regulator. The 1Nxxx across the pass element does nothing to prevent reverse current from the output caps, into the e, out of the b, at switch off. The danger of repeating a piece of text from another post is that it may have nothing to do with the issue at hand, unless you really understand it.
Jan Didden
Resistors vs diodes.....
Diodes can be added in series with the zener to add some stability wrt temperature. In this circuit, it adds one diode drop to compensate for the output drop. So the output is closer to the actual zener voltage.
Everyone has their own design criteria, but I usually go for maximum PSRR without going to ridiculous extremes.
But that is just my preference........doensn't mean that it is law.
Jocko
Diodes can be added in series with the zener to add some stability wrt temperature. In this circuit, it adds one diode drop to compensate for the output drop. So the output is closer to the actual zener voltage.
Everyone has their own design criteria, but I usually go for maximum PSRR without going to ridiculous extremes.
But that is just my preference........doensn't mean that it is law.
Jocko
I have made this supply you referred to, the one from tnt-audio. It works fine for me. I used the BD139/BD140, but it would be better to use the BC550/BC560 and the BD139/BD140 in a darlington configuration (as Rod Elliot also suggests in his capacitance multiplier (http://sound.westhost.com/project15.htm))
I didn't include the R13 resistor, but simulations show that this would improve ripple rejection a bit. The value to choose is dependant on supply voltage and current demands.
For the capacitance on the output I used a standard grade 1000uF and for the input 4700uF. Works fine.
For R14 I used a smal pot of 200 or 300 ohm to set the voltage to the desired value. In the range of 14.5 to 15.5 in my case.
I made R15 a bit smaller to provide my zener with enough current, but this depends on your zener.
The problem I had with this supply in ,this thread had something to do with my tranny. I think the lower loading makes it noisy. I solved this by putting it outside my case.
A nice article I found on this subject can be found here.
The URL of the website of the above article is http://www.engin.umd.umich.edu/~fmeral/ .
I hope this helped,
Cheers
I didn't include the R13 resistor, but simulations show that this would improve ripple rejection a bit. The value to choose is dependant on supply voltage and current demands.
For the capacitance on the output I used a standard grade 1000uF and for the input 4700uF. Works fine.
For R14 I used a smal pot of 200 or 300 ohm to set the voltage to the desired value. In the range of 14.5 to 15.5 in my case.
I made R15 a bit smaller to provide my zener with enough current, but this depends on your zener.
The problem I had with this supply in ,this thread had something to do with my tranny. I think the lower loading makes it noisy. I solved this by putting it outside my case.
A nice article I found on this subject can be found here.
The URL of the website of the above article is http://www.engin.umd.umich.edu/~fmeral/ .
I hope this helped,
Cheers
When I asked Werner about placing the cap at the BJT's base, and increasing the base resistor to a few hundred ohms, he told me that it was a bad idea, and would "murder" the output impedance
But I don't understand why. I thought that a LP filter would be a good idea.
Does anybody know?
But I don't understand why. I thought that a LP filter would be a good idea.
Does anybody know?
I am quite aware this is not a 3 terminal regulator, Jan. Did you read the word "also"? That comment was directed to a neophyte designer.janneman said:
As to the diode across base-emitter, poppycock! It is not likely for current to flow from emitter to base of the pass transistor when the input voltage is switched off. The base sees a zener and a reference bypass capacitor to ground. When input voltage decreases the zener essentially opens, while the load drains the output cap and gradually drains the reference bypass cap.
I can envision pathological cases in which reverse current could flow: an intentional or accidental short of the input or bypass cap to ground, or connecting the output to a higher voltage supply. You cannot guard against every act of lunacy and you should not attempt to do so.
Every part you throw into a circuit can reduce its reliability and add cost from a manufacturing and maintenance viewpoint. It's not merely elegant to keep things simple, it's solid design practice for real world engineers.
For the life of me I can't see why this design is being considered, unless it is purely for educational purposes. This design can easily fail and take out the entire load instantly.
Adjustable 3 terminal regulators have been ubiquitous in electronic products for several decades. They are far better regulators than this circuit, and have short circuit protection. To me they seem a much better design choice.
Had I guessed the amount of confusion this article would cause ...
First and foremost: the article series is a just a quick enquiry into output noise of a number of simple regulator topologies. No more, no less. It certainly is not a tutorial on regulator design, and the schematics shown are no more than conceptual sketches. It is clear now that I should have emphasised that.
So again now, and referring to the TNT-sourced little green schematic...
In the zener-follower thingy, R13 plays no role. It is a left-over of my copying-and-pasting from other circuits. However, a lower-value R13 followed by a large-value C to ground 1) would increase PSRR a lot, and 2) would protect the pass transistor at start-up from over-current into C7. This is not unimportant as a low-ESR 220uF can and will fry that transistor on a bad day if no precautions are taken.
Base resistor R17 is just high enough to assure stability. Making it higher serves no purpose and deteriorates output impedance somewhat. In other words, I want the base to be driven from the relatively low source impedance formed by R17 and C8.
I have R17 in series with the zener as I needed a particular level shift and was not prepared to put in a string of additional diodes. R17 is very important to filter out zener noise, but as others have mentioned, there are other places to put it just as well if no level shift, or a better PSRR, is desired.
Just in case anyone wondered about the 100Hz harmonics in the noise spectrum: these were induced by the close proximity of an unshielded toroid. Moving the regulator board yields a flat noise trace.
First and foremost: the article series is a just a quick enquiry into output noise of a number of simple regulator topologies. No more, no less. It certainly is not a tutorial on regulator design, and the schematics shown are no more than conceptual sketches. It is clear now that I should have emphasised that.
So again now, and referring to the TNT-sourced little green schematic...
In the zener-follower thingy, R13 plays no role. It is a left-over of my copying-and-pasting from other circuits. However, a lower-value R13 followed by a large-value C to ground 1) would increase PSRR a lot, and 2) would protect the pass transistor at start-up from over-current into C7. This is not unimportant as a low-ESR 220uF can and will fry that transistor on a bad day if no precautions are taken.
Base resistor R17 is just high enough to assure stability. Making it higher serves no purpose and deteriorates output impedance somewhat. In other words, I want the base to be driven from the relatively low source impedance formed by R17 and C8.
I have R17 in series with the zener as I needed a particular level shift and was not prepared to put in a string of additional diodes. R17 is very important to filter out zener noise, but as others have mentioned, there are other places to put it just as well if no level shift, or a better PSRR, is desired.
Just in case anyone wondered about the 100Hz harmonics in the noise spectrum: these were induced by the close proximity of an unshielded toroid. Moving the regulator board yields a flat noise trace.
3-terminal regulators are better......
For what? Maybe absolute DC accuracy......short-circuit protection.......low z at low frequencies.
So what?? Ever listen to one? And compare it to anything else???
Yeah, maybe a good choice for some industrial product. Maybe not for audio.
Don't discount simple followers, just because some so-so examples are in this thread.
Jocko
For what? Maybe absolute DC accuracy......short-circuit protection.......low z at low frequencies.
So what?? Ever listen to one? And compare it to anything else???
Yeah, maybe a good choice for some industrial product. Maybe not for audio.
Don't discount simple followers, just because some so-so examples are in this thread.
Jocko
a few ohms for R1/R11
put a 4.7k resistor at the 2nd transistor base to ground
I'd say give 4 or 5V dropout to the regulator
1000uF seems big, I'd put 100 of 200 instead
put a 4.7k resistor at the 2nd transistor base to ground
I'd say give 4 or 5V dropout to the regulator
1000uF seems big, I'd put 100 of 200 instead
Bricolo said:
Agreed. But he also needs an extra diode in each of the diode-zener strings to compensate for the extra b-e junction drop, to get back to 15V nominal.
Jan Didden
Bricolo said:
What does the 4k7 do?
janneman said:
The 15V isn't that important, as long as it's under 18V. 🙂
Alcaid said:
Pulls 3mA from the BC550 so that its own output impedance drops to
about 10 Ohms.
BTW, how much current does your load demand?
I'm going to use it for 2x OPA627 and 2x BUF634T in wide BW mode. Don't actually need more than 44-55mA then pluss 50mA for the dummy load. (I think).
Hello Alcaid, How about this one?
You can use the LM431 or a Sziklai connection in place of the Darlington. A constant current source for the reference improves the sound. If you use an inductor in place of R1 (in your scheme)you will get better ripple rejection.😎
You can use the LM431 or a Sziklai connection in place of the Darlington. A constant current source for the reference improves the sound. If you use an inductor in place of R1 (in your scheme)you will get better ripple rejection.😎
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