Zener regulator with "integrated" pre-regulator - diyAudio
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Old 14th July 2008, 02:04 PM   #1
00940 is offline 00940  Belgium
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Default Zener regulator with "integrated" pre-regulator

Does the following schematic look ok to you ? The lm317 is both used as preregulator and CCS (the adjust leg) for a typical zener+pass transistor reg.
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Old 14th July 2008, 03:54 PM   #2
Corax is offline Corax  Germany
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I see no benefits at all !!!

The schematic might work - if you've successfully simulated it.

The output voltage might be well regulated, concerning ripple rejection from the mains, but the output voltage itself is not 'really' regulated. In fact it will vary with temperature, etc. based on the fact that Q1/Q2 acts as a Darlington emitter-follower and that there's no feedback from the output.
What should this circuit basically do for you???
I don't really 'see' an application where this circuit is desired - so please explain what you had in mind and why you've designed it. What should be the goal for that circuit?
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Old 14th July 2008, 04:15 PM   #3
00940 is offline 00940  Belgium
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Quote:
Originally posted by Corax
The output voltage might be well regulated, concerning ripple rejection from the mains, but the output voltage itself is not 'really' regulated. In fact it will vary with temperature, etc. based on the fact that Q1/Q2 acts as a Darlington emitter-follower and that there's no feedback from the output.

What should this circuit basically do for you???
I don't really 'see' an application where this circuit is desired - so please explain what you had in mind and why you've designed it. What should be the goal for that circuit?
Well, I know what a darlington is and I know the circuit will drift a bit. It is also quite clear it has no feedback.

Aim of the circuit ? Feed a discrete I/V stage.

What I had in mind ? Try first something else than the usual lm317, with better high frequency rejection. Secondly, try to improve the local regulators used by rbroer on his I/V : http://www.diyaudio.com/forums/attac...amp=1068412889
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Old 14th July 2008, 04:36 PM   #4
Corax is offline Corax  Germany
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Well, for this intended purpose I guess the circuit is OK.
No feedback won't make any trouble with oscillation tendencies, basically.
The only weak point is still the use of the LM317 which is a little bit noisy in my opinion. Use a low-noise reference element and a more traditional regulator design with transistors and I'll vote for your design.

On the other side your design would be fine if I would consider the parts count and PCB space necessary for a traditional design. So, under some aspects your design is flawless and it'll do what it's supposed to do.
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Old 15th July 2008, 02:03 PM   #5
00940 is offline 00940  Belgium
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Hum, reading myself again, the tone was a bit harsh, sorry.


On a more "conventionnal" way of doing a regulator, here's another option I'm considering (the PS being bipolar, I'll use a ne5532 and will have a negative supply available):
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Old 15th July 2008, 02:40 PM   #6
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If you use an opamp that can work with the supply you have (+15? +5?) there's no need for a negative supply. Just ground the -supply pin.

Actually, you seem to be on the road to reinvent the 'super-regulator' with pre-regulator

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Old 15th July 2008, 03:19 PM   #7
Corax is offline Corax  Germany
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@00940:
I didn't feel that your tone was a bit harsh.
Since I couldn't find any information about your education(s), skills, etc. I can only guess about someones knowledge and that you're a PSCI(?) student doesn't make any sense to me because I don't know what this abbreviation stands for. Sometimes I've just a feeling that he/she knows a lot sometimes not. The latter case I assumed in your case I must admit. So I guess I have to apologize.

Nevertheless your last design is much better and I agree with Jan to omit the negative supply for the OpAmp.
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Old 15th July 2008, 03:33 PM   #8
00940 is offline 00940  Belgium
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Quote:
Originally posted by janneman
Actually, you seem to be on the road to reinvent the 'super-regulator' with pre-regulator

Jan Didden
Well, maybe but I don't think I'm willing to go further down the road There are still some major differences, though (better opamp, way to provide current to the voltage reference, better voltage reference, a few caps and resistors, gain for the voltage reference, etc.).

The PS should give around +/-16.7VDC as is (easily changed by changing the zener value). Bad news is the heavy dropout at around 6.5VDC minimum.
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Old 16th July 2008, 04:04 PM   #9
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Wrt the negative voltage: I'll be building both positive and negative supplies, so I'll have one available. The whole thing will be more compact with a ne5532 with +/- supplies. The operating voltage is close to the limit though... about +/-20VDC.


@Corax: I should update my profile, it's a few years old now. PSCI stood for political science (it was rather stupid to put that into the profile I admit) but I'm now working for the Jesuit Refugees Service. Nothing related to electronics as you can see
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Old 16th July 2008, 04:46 PM   #10
AndrewT is offline AndrewT  Scotland
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the 5534 & 5532 can take about 42V across the supply pins.
20V is well within this limit.
But you are asking the opamp to operate with the input pin voltage very close to the positive supply rail. They are not rail to rail opamps.

Take the hint from Janneman and go and read up on super regulators at Walt Jung's site.
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