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Old 21st August 2002, 11:20 PM   #21
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Default Rehabilitated?

Maybe it is just that Grey isn't here to tell everyone how evil I am
I have posted schematics and lots of info for a long time.

H.H.
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Old 22nd August 2002, 01:17 AM   #22
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Default Basic shunt regulator topology

DZ2 only used if regulated Vout is greater than maximum supply voltage for A1. R1 could be current source for greater PSRR.
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Old 22nd August 2002, 04:29 AM   #23
Kevinbd is offline Kevinbd  United Kingdom
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Default Shunt Regulator

Hello,

I have thought of running my power amp with a shunt regulator before.

Can a shunt regulator reduce output impedance like a series regulator?

The current source has high output impedance of course.

Or would it still need to be fed from a series regulator to get the lower impedance ?

The load is constant at 2A 24V. (single ended)

Kevin
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Old 22nd August 2002, 06:17 AM   #24
ALW is offline ALW  United Kingdom
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Default Modding for 5V

As Harry suggests, an op-amp suitable for 5V operation is the first thing to find.

AD825 looks promising here.

Then a 2.5V low-noise reference is required. WJ suggests some AD parts, I have a unit running from a TL431, set to min o/p of 2,5V.

In this state the TL431 noise is low, and unamplified by it's own loop gain - about the only good use I've found for TL431's

MY one is using an OP27, which I'm not sure is specified for 5V, but works well nonetheless.

Maybe Jan could offer some devices to try, failing that the important criteria are high open-loop gain over the widest BW and low voltage noise, along with a good element of DC stability.

Andy.
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Old 22nd August 2002, 07:32 AM   #25
Faber is offline Faber  Italy
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This is what I use to feed my amp.

I have found this schematic on the net and slightly modified it.
It's a op-amp, as you can see, and you can modify the gain by working on R5/R4 ratio for the positive rail and on r17/R16 ratio for the negative rail.

The circuit has a very low ripple and a good stability, but if you find some bugs... I will appreciate your advices :-)

My 2 cents, bye!
Fabrizio
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Old 22nd August 2002, 09:57 AM   #26
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Lightbulb AD825 looks promising

The AD 825 requires + and - 5volts supplies, I was leaning toward single suppy op amps. The TL431 still a little noisy, how about an LED biased with a current source afor a reference?

Some single 5V supply op amps that might work are:
LT6203
LT1812
EL2120C

H.H.
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Old 22nd August 2002, 10:09 AM   #27
ALW is offline ALW  United Kingdom
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Default AD825

Harry if you look at the spec sheet - you'll see it's partially specced to +/-2.5.

It's only fully characterized for +/-5.

Don't forget the reference is filtered quite heavily, and hence even the 431 works well here - still much quieter at the reg o/p that anything off-the shelf, by a tens of dB

A.
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Old 22nd August 2002, 10:18 AM   #28
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Red face Harry if you look at the spec sheet

I will concede.I did a quick look at the data sheets but it looks like you have done your homework more thoughly than I. Checkout the single supply opamps that I have mentioned also.
Bygones?

H.H.
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Old 22nd August 2002, 10:33 AM   #29
ALW is offline ALW  United Kingdom
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Default AD8610?

I haven't checked, but the oft-talked-about AD8610 models superbly in the Jung circuit - IIRC it has lower upper voltage limits than most.

It may have lower bottom end limits too (I've not checked yet).

Looks superb in the SPICE sim.

A.
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Old 22nd August 2002, 10:40 AM   #30
ALW is offline ALW  United Kingdom
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Default Wierd stuff

OL gain for the AD8610 looks very low, I can't understand why impedance plots are so good.

Data sheet or model error perhaps?

A.
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