Improving the LM3x7 regulator circuit - Page 16 - diyAudio
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Old 8th January 2012, 09:58 AM   #151
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Hi Zack, R12 and R13 are to provide a minimum current draw for the reglulator. The reason there are two is because it was easier for me to get 1/2 w resistors than 1W ones, and I didn't want them getting too hot. I'm pretty sure it was Jan Didden that said that LM317's performed better with a certain amount of current draw, but I can't find the reference. The idea for the resistors is to provide a minimum constant draw of around 40mA to ensure the reg stays in a better performance zone.

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Old 8th January 2012, 10:34 AM   #152
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Everyone seems intent on getting the noise level from the supplies down to less than zero.

However, in Hi-End Hi-Fi use I personally can't hear any noise from the humble LM317.

In my simple circuit I simply wanted 18V at about 20mA for a Pre-Amp.

The results are an Audio Blackness (SILENCE) that I can not see any point in bettering.

Point of note - anyone wishing tio try this circuit, please insert a 1K in series with R2 (without it there is a danger of frying the zener if R2 is adjusted to its minimum).

Maybe I've just got everything right and the Pre has a high PSRR. But why make it any better than it already is ?

Incidentally the LED is there to increase the output current to approx 25mA, as well as to serve as an indicator.
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Old 8th January 2012, 10:55 AM   #153
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fair comment KatieandDad I think SY commented in my experiments and measurements thread that at some point it ceases to be about improving anything audibly and becomes solely an exercise in engineering.

Obviously some circuits will have better PSRR than others. I took the approach if it's not there then it can't cause a problem I did say it was overkill

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Old 8th January 2012, 12:03 PM   #154
AndrewT is online now AndrewT  Scotland
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The upper 1n400x caters for back emf bypass when the transformer shuts down. Keep it.
The lower 1n400x caters for back emf when the regulator shuts down and is needed to discharge the cap smoothing the ADJ pin. 10nF does not require that extra diode protection to be added. 100uF across the Zener would require the extra diode.
The voltage from OUT to ADJ (if the regulator is not broken) is ~ 1250mV.
The current from OUT to Zener cannot exceed 1250mV/220r ~ 5.7mA
The worst case dissipation in the Zener is ~ 57mW.
In normal stop start run operation no setting of the 5kVR can damage the Zener.

@ 18V output the 6k8 has ~ 16V across it. The current passing to the LED is ~ 2.4mA

The total demand from the OUT PIN is ~ 2.4mA + 5.7mA + load current. The load current must equal or exceed 16.9mA at all operational conditions for the 25mA desired REG load to be true.
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Old 8th January 2012, 01:56 PM   #155
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Quote:
Originally Posted by AndrewT View Post
The upper 1n400x caters for back emf bypass when the transformer shuts down. Keep it.
The lower 1n400x caters for back emf when the regulator shuts down and is needed to discharge the cap smoothing the ADJ pin. 10nF does not require that extra diode protection to be added. 100uF across the Zener would require the extra diode.
The voltage from OUT to ADJ (if the regulator is not broken) is ~ 1250mV.
The current from OUT to Zener cannot exceed 1250mV/220r ~ 5.7mA
The worst case dissipation in the Zener is ~ 57mW.
In normal stop start run operation no setting of the 5kVR can damage the Zener.

@ 18V output the 6k8 has ~ 16V across it. The current passing to the LED is ~ 2.4mA

The total demand from the OUT PIN is ~ 2.4mA + 5.7mA + load current. The load current must equal or exceed 16.9mA at all operational conditions for the 25mA desired REG load to be true.
WAFFLE-WAFFLE-WAFFLE.

It works and the design is perfect, other than the possibility of damaging the zener without the extra resistor with R2.

I used this to replace the Shuntkys while I was trying to get my Pumpkins to work.

Do bear in mind that my load has over 30000uF in it and draws over 20mA in its own right.

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Old 8th January 2012, 02:10 PM   #156
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There were two areas that were proposed here to improve and the reason for this topic:

1) The adjustment pin arrangement, where a transistor was added.

2) The output capacitor, where a resistor was added in series with it.

The 3X7s do not seem to like low-esr capacitor types, and the series resistor corrected that, allowing using any cap.

OTOS the 3X7s do not like too much capacitance, so if you are using 30,000uF as you say you are, that would go against many people that think otherwise.
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Old 8th January 2012, 02:13 PM   #157
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Regardless. It works beautifully.

You can go only so far with theory then practicality takes over.

There is a 1R5 in series with the supply which might make a difference.
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Old 8th January 2012, 05:27 PM   #158
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here is a foto of one of my lm317 regs.........only a z-diode (16v) is in series with the adj. pin.
res at the output is 220 ohm.
i use it with my headphone amp and so on. works without problems.
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Old 8th January 2012, 08:08 PM   #159
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Quote:
Originally Posted by KatieandDad View Post
Regardless. It works beautifully.

You can go only so far with theory then practicality takes over.

There is a 1R5 in series with the supply which might make a difference.
Things working beautifully may just mean that it's just doing its primary job:regulate

But I think what we are trying to do here is make things better. By that I mean "sound better". Which is hard to prove because it's mostly a subjective thing.

Theory is what this topic started to do and DIY by definition means make things practical.

If you are putting a series resistor after the regulator, you're probably invalidating one of the important objectives, which is lowering impedance.

One of the first thing that was done in CD player mods in the '80s was just eliminate every series resistor after regulators that manufacturers insisted to put.
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Old 22nd December 2012, 08:33 AM   #160
Jenyok is offline Jenyok  Russian Federation
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Quote:
Originally Posted by Fred Dieckmann View Post
It really is worth using a current in between Vout and ADJ since the variation of the 1.25 volt reference in the regulator IC is the main contributor to PSRR and output impedance degradation. I have a circuit that should work pretty well with easily available parts. The transistors can be any thing with a very high Hfe at a milliamp or two. C1 should be a film cap and you can get away with something like 1uF if you what. I believe the voltage out is about 15 volts for the resistor values shown. I also have another design with a current jfet and a diode thermally coupled to the regulator with copper tape. The thermally coupling and the likely hood that you don't have a jfet CCS in your parts box may make this an easier circuit. You could get rid of Q1 and Q2 and put a resistor across Vout to ADJ but the performance of the circuit is not as good as with the current source.
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Please, put here circuit of "another design with a current jfet and a diode thermally coupled to the regulator with copper tape".
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