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'[EE] Amplified diode regulator'
2007\10\31@103225 by Tamas Rudnai

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part 1 307 bytes content-type:text/plain; charset=ISO-8859-1 (decoded 7bit)

Hi,

I was thinking about regulating the Vdd using an amplified diode circuit.
Basically the input voltage could be varied between 4-7.2V and I am going to
set this circuit to 3.3V. The load is around 1-2mA. I was wondering if there
is any con about this?

Thanks,
Tamas


part 2 16850 bytes content-type:image/jpeg; name=regulator_amplified_diode.JPG (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2007\10\31@110603 by David VanHorn

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> I was thinking about regulating the Vdd using an amplified diode circuit.
> Basically the input voltage could be varied between 4-7.2V and I am going to
> set this circuit to 3.3V. The load is around 1-2mA. I was wondering if there
> is any con about this?

As shown, this is not a regulator.
I think what you're intending is an emitter follower on a zener
regulator, but a single component monolythic solution would be much
better, and probably more efficient as well.

2007\10\31@111918 by Bob Axtell

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David VanHorn wrote:
>> I was thinking about regulating the Vdd using an amplified diode circuit.
>> Basically the input voltage could be varied between 4-7.2V and I am going to
>> set this circuit to 3.3V. The load is around 1-2mA. I was wondering if there
>> is any con about this?
>>    
>
> As shown, this is not a regulator.
> I think what you're intending is an emitter follower on a zener
> regulator, but a single component monolythic solution would be much
> better, and probably more efficient as well.
>  
I think his verbiage is correct, tho... he is amplifying a  zener diode.
At 2mA you could use a 3.3V
zener by itself, methinks.

A LM317 would be a better device, agreed.

--Bob

2007\10\31@120536 by Michael Rigby-Jones

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>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu]
>On Behalf Of Tamas Rudnai
>Sent: 31 October 2007 14:32
>To: Microcontroller discussion list - Public.
>Subject: [EE] Amplified diode regulator
>
>
>Hi,
>
>I was thinking about regulating the Vdd using an amplified
>diode circuit. Basically the input voltage could be varied
>between 4-7.2V and I am going to set this circuit to 3.3V. The
>load is around 1-2mA. I was wondering if there is any con about this?
>
>Thanks,
>Tamas
>

For a tradional amplified diode arangement, the top of R2 should be connected to the collector of the transistor.

The disadvantages are the same as zener diodes, soft knee (poor line and load regulation) and poor tempco etc. but typicaly somewhat worse again.

A linear pass regulator is very likely a better solution.  They are cheap and their performance will be in a different league.

Regards

Mike

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2007\10\31@120752 by Michael Rigby-Jones

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{Quote hidden}

An amplified diode can use Vbe to do the regulating.  A potential divider connected accross the collector and emitter feeds a fraction of Vce to the base, thus you get some multiple of Vbe appearing accross Vce (the OP's circuit is not quite correct).  A fairly low performance circuit anyway.

Regards

Mike

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2007\10\31@122953 by Spehro Pefhany

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Quoting Tamas Rudnai <EraseMEtamas.rudnaispam_OUTspamTakeThisOuTgmail.com>:

> Hi,
>
> I was thinking about regulating the Vdd using an amplified diode circuit.
> Basically the input voltage could be varied between 4-7.2V and I am going to
> set this circuit to 3.3V. The load is around 1-2mA. I was wondering if there
> is any con about this?
>
> Thanks,
> Tamas

As Mike says, you can use a "Vbe multiplier" circuit (2 resistors and a
BJT) as shunt regulator. Cons include poor temperature coefficient (-0.3%/K)
poor initial voltage accuracy and poor line/load regulation, plus
it will waste power since you will probably have to give it 3mA or so
regardless of the load. A couple of red LEDs in series might work out better
if you want to do that sort of thing, or just put a proper regulator in there.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
s...spamspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



2007\10\31@123137 by Russell McMahon

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The circuit as shown would be unsatisfactory.

A variable (programmable I believe they call it) LM385
precision shunt regulator would do the job at not vastly
more cost and in a far superior manner.



       Russell

> I was thinking about regulating the Vdd using an amplified
> diode circuit.
> Basically the input voltage could be varied between 4-7.2V
> and I am going to
> set this circuit to 3.3V. The load is around 1-2mA. I was
> wondering if there
> is any con about this?

2007\10\31@200254 by Russell McMahon

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> A linear pass regulator is very likely a better solution.
> They are cheap and their performance will be in a
> different league.

Probably. But there are several shunt regulator diodes
around that are ultra cheap because they are used in
zillions. The LM385 is cheapish and the lower spec TL431 is
about the cheapest IC you can buy, ($US0.40/1 down to under
$US0.08/large_volume).

FWIW the lovely CD40106 is just dearer at high volume and at
under $US0.015 a Schmitt inverter may be the best value IC
ever known.  Not so good as a voltage regulator though :-)



       Russell


'[EE] Amplified diode regulator'
2007\11\01@051454 by Tamas Rudnai
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Thanks everyone for the suggestions. In the meantime I realised it is so
sensitive with the load (R3 on that simulation I attached in the original
post). With the R2, yes, I know in the original circuit it should be
connected to the collector, however, I used a modified version of it (the
idea is coming from this proceeding:
http://www.essex.ac.uk/dces/research/audio_lab/malcolmspubdocs/J8%20Optimization%20of%20the%20amplified%20diode.pdf)

Anyway, a zener with an emitter follower would be sufficient enough but then
the cost comparable to those regulators you guys mentioned, so I'll give
them a go. BTW this project is quite cost sensitive and also have a limited
size.

Thanks again,
Tamas


On 11/1/07, Russell McMahon <@spam@apptechKILLspamspamparadise.net.nz> wrote:
{Quote hidden}

> -

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