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'[OT] Interesting discrete device?!'
1999\12\02@023000 by Don Holtz

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Hello:

I was recently in Japan, and visited Akihabara.  While there I picked up a
handful of really bright White LEDs.  With each LED the vendor also gave me
an interesting discrete device that looks like a standard small-signal
glass encapsulated diode.

I don't speak Japanese but I was able to get the vendor to draw a simple
schematic, since I was confused about the device.

The device appears to be a "current regulating diode" analogous to a
zener.... 15mA!

In this instance the LED and "current regulating diode" are placed in
series, and the combination can be driven with a voltage between 4V and 20V.

Further testing shows that below the "turn on" current level the device has
a fairly low impedance (approx. 200ohm), above the "turn on" current level
the device has a fairly high impedance of more than 100Kohm.

The only marking on the device is E153.

The symbol the vendor used in the schematic was a circle with a bar, kind
of like an arrow head with a bar (for a diode).

What is this device?  Am I missing something simple?

Cheers,
Don

1999\12\02@054500 by Thomas C. Sefranek

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Don Holtz wrote:

{Quote hidden}

It's an FET connected as a constant current diode.
(Classic jfet and resistor in the source lead.)
Motorola had these for several values of current many years ago.

>
>
> Cheers,
> Don

--
Thomas C. Sefranek  WA1RHP
ARRL Instructor, Technical Specialist, VE Contact.
http://www.harvardrepeater.org
http://hamradio.cmcorp.com/inventory/Inventory.html

1999\12\02@055750 by Mark Willis

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You can make a current limiter out of an LM317 with a resistor across
the "Output" and "Reference" terminals, if they just packaged such a die
with the resistor as a 2-terminal package, that sounds about like what
you have there.  Nice discrete, it makes GOOD sense to use those for
LED's, wish I had some here! <G>  Great for a number of applications.
Car tail light LED units, for one.

Related question;  Wonder what happens when one parallels these
devices?  <G>  I'd think the "conductances" would add, 2 paralleled 20mA
units should let about 40mA flow, but I haven't tested it yet.  Should
get to that some day <G>

 Mark

Don Holtz wrote:
{Quote hidden}

--
I ship small packages for small businesses, world-wide.
(And for private individuals at cost, just ask.)

1999\12\02@073315 by Michael Rigby-Jones

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part 0 4034 bytes
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Standard two terminal current source.&nbsp; It's effectively a FET with the gate tied to (I think) the source.</FONT>
</P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Regards</FONT>
</P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Mike Rigby-Jones</FONT>
</P>
<UL>
<P><FONT SIZE=1 FACE="Arial">{Original Message removed}

1999\12\02@092935 by William K. Borsum

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I think this, or something very like it is still available--look in the
diode section of the mouser and digikey catalogs--I know I bought a variety
a year or so ago.  Not real precise--3-5%, but available in current ranges
from 1 or 2 ma up.  however, NOT cheap.
Kelly



At 02:56 AM 12/2/99 -0800, you wrote:
{Quote hidden}

20V.
{Quote hidden}

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<spam_OUTborsumTakeThisOuTspamdascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\12\02@105213 by Jason Harper

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> The device appears to be a "current regulating diode" analogous to a
> zener.... 15mA!

They're also known as "constant current diodes", or "field effect diodes".

The standard part numbers for them are around 1N5300, depending on the
current rating.  Very nifty devices: I guess the only reason you don't see
them used all over the place is that they seem to cost at least $4 each in
small quantities...  (I'd be REALLY happy if someone proved me wrong on
that, I would like to use some in an upcoming project.)

You can find some info on CRDs at:
http://www.intlsemiconductor.com/catalogs.htm

> You can make a current limiter out of an LM317 with a resistor across
> the "Output" and "Reference" terminals

Yes, but with a limitation compared to a CRD: the LM317, and all other
similar regulators I've found that support this use as a current regulator,
require about 5-10 mA of current flow to maintain regulation.  When used in
the normal voltage regulator mode, it's easy to pick resistor values that
will pass that much current to ground if you aren't sure that your load
will.  However, in current regulator mode there's no connection to ground,
so all that current has to go through your load.  CRDs, on the other hand,
are available with ratings down to under 1 mA.

Another advantage of CRDs in certain applications is that they can safely
drop up to 100 volts, assuming that this doesn't exceed the power
dissipation limit.  Few 3-terminal regulators can handle more than about a
30 volt drop.

> Related question;  Wonder what happens when one parallels these
> devices?  <G>  I'd think the "conductances" would add, 2 paralleled 20mA
> units should let about 40mA flow, but I haven't tested it yet.  Should
> get to that some day <G>

According to the reference I mentioned above, you can connect CRDs in
parallel for increased current without any special precautions.  The
individual ratings don't even have to match, they simply add together.  Of
course, given how much CRDs cost, I can't imagine many people taking
advantage of this feature...
       Jason Harper

1999\12\02@162401 by paulb

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Mark Willis wrote:

> You can make a current limiter out of an LM317 with a resistor across
> the "Output" and "Reference" terminals,

 Limitation here is the combined minimum input-output differential
*plus* the 1.25V reference voltage, means minimum drop is about 3.25V or
so.  I suspect the CRDs may have a lower minimum drop?

 And as mentioned, the minimum current in this mode is set by the
reference current which for an LM317 is 50 to 100 µA, plus the swamping
current which is usually at least 1 mA.  You *can* therefore use an
LM317 for as little as 1 mA with some limitation on accuracy.

 I'm sure the LM317 has a far higher power dissipation than the CRDs.

> Nice discrete, it makes GOOD sense to use those for LED's, wish I had
> some here! <G>  Great for a number of applications.

 Cost has been mentioned.  That slows down the enthusiasm.  We can't
all visit Aki. :-((

>  Car tail light LED units, for one.

 That is *definitely* a high-power application.  I'd look to the LM317
if you want simplicity, but the traditional 3-terminal circuits can
achieve a 1V or so minimum drop which is difficult to beat.

> Related question;  Wonder what happens when one parallels these
> devices?  <G>  I'd think the "conductances" would add, 2 paralleled
> 20mA units should let about 40mA flow, but I haven't tested it yet.

 It *must* work fine - by definition.
--
 Cheers,
       Paul B.

1999\12\02@163850 by paulb

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Jason Harper wrote:

> the LM317, and all other similar regulators I've found that support
> this use as a current regulator, require about 5-10 mA of current flow
> to maintain regulation.

 Whoops!  Just came across that specification.  3.5mA typical, 5mA
guaranteed for the LM317.
--
 Cheers,
       Paul B.

1999\12\02@172543 by Mark Willis

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Paul B. Webster VK2BZC wrote:
>
> Jason Harper wrote:
>
> > the LM317, and all other similar regulators I've found that support
> > this use as a current regulator, require about 5-10 mA of current flow
> > to maintain regulation.
>
>   Whoops!  Just came across that specification.  3.5mA typical, 5mA
> guaranteed for the LM317.
> --
>   Cheers,
>         Paul B.

NOT a problem for use in a car tail light LED setup where you want 20mA,
that TO220 package size would be though <G>  LM317LZ is in TO92, but you
need that plus 2 resistors plus a Transzorb to protect it all plus maybe
a choke, that's getting a little large for a #194 bulb <G>  Would fit
the 1156 and barely the 1157's, I guess.  (Have to use 2 setups in
parallel for the 1157, each with it's own LED's, I guess?)  Maybe just
go to a 12C509A circuit anyways & PWM the LEDs, to get enough
brightness...

Never a simple solution <G>

 Mark

--
I ship small packages for small businesses, world-wide.
(And for private individuals at cost, just ask.)

1999\12\03@000443 by Aaron Hammett

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>>The device appears to be a "current regulating diode" analogous to a
>>zener.... 15mA!

>>In this instance the LED and "current regulating diode" are placed in.
>>series, and the combination can be driven with a voltage between 4V and 20V.

>>Further testing shows that below the "turn on" current level the device has
>>a fairly low impedance (approx. 200ohm), above the "turn on" current level
>>the device has a fairly high impedance of more than 100Kohm.

>>The only marking on the device is E153.

>>The symbol the vendor used in the schematic was a circle with a bar, kind
>>of like an arrow head with a bar (for a diode).

>>What is this device?  Am I missing something simple?

 I first saw this device in a Kenwood automotive audio amplifier about three
years ago, while testing the constant current source in the pre driver stage.
I thought it was defective, since it didn't measure properly..and seemed
leaky. In the Kenwood KAC-820 service manual, it's listed as--none other
than--Constant Current Diode E-153. It's used in this circuit with an NPN
transistor between emitter and base, with no current limiting resistor (of
course).

1999\12\03@003615 by Don Holtz

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I am surprised that these CRD devices do not see more wide spread use.  I
am familiar with using a FET/JFET as current limiters, but I was not aware
that a nice and simple 2 terminal device was availabe to do the job... off
the shelf!!  Terrific!

As for price... I paid 200yen (approx US$2) for the super-bright white LED,
and the CRD was thrown in for free.  I can't imagine that they (the CRD's)
are not worth too much compared to the cost of white LEDs?!

I wish I had bought more... the LEDs are incredible (as far as LEDs go!).
And the CRDs are extremely interesting and useful!

If CRDs were avaiable for a reasonable price (<$1) they could be used in
many designs.  What range of prices have people seen for them?

On a more practical note, I suspect that when a CRD fails... it becomes a
good short circuit.

Cheers,
Don




At 08:22 AM 12/3/99 +1100, you wrote:
{Quote hidden}

1999\12\03@014855 by Harold M Hallikainen

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       With all the talk about current regulator diodes being biased FETs...
isn't there just a plain old diode that is optimized as a current
regulator?  As I recall, all diodes exhibit nearly constant current
behavior when reverse biased (until they reach the zener voltage).
Aren't some of the current regulator diodes just diodes optimized for
this purpose?
       Second, why use them to drive an LED?  If you have a relatively stable
voltage source, and the LED voltage is relatively stable, a resistor
serves as a voltage to current converter to drive the LED.  Are one of
these voltages changing, thus requiring the current regulator diode?
       I still want to experiment with driving an LED with the flyback current
off an inductor.  We'd have a circuit similar to a standard relay driver
with a diode across the coil, only the diode would be the LED and the
coil would be an inductor.  During the inductor "charge" time, the LED
would be back biased.  When the transistor is off, the inductor current
would ramp down through the LED (or several in series).  Seems like an
efficient way to drive an LED, since there's no resistor wasting power.

Harold


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1999\12\03@081825 by Michael Rigby-Jones

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<P><FONT SIZE=2 FACE="Arial">&gt; You can make a current limiter out of an LM317 with a resistor across</FONT>
<BR><FONT SIZE=2 FACE="Arial">&gt; the &quot;Output&quot; and &quot;Reference&quot; terminals,</FONT>
</P>
</UL>
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Paul Webster replied:</FONT>
</P>
<UL>
<P><FONT SIZE=2 FACE="Arial">&nbsp; Limitation here is the combined minimum input-output differential</FONT>
<BR><FONT SIZE=2 FACE="Arial">*plus* the 1.25V reference voltage, means minimum drop is about 3.25V or</FONT>
<BR><FONT SIZE=2 FACE="Arial">so.&nbsp; I suspect the CRDs may have a lower minimum drop?</FONT>
</P>

<P><FONT SIZE=2 FACE="Arial">&nbsp; And as mentioned, the minimum current in this mode is set by the</FONT>
<BR><FONT SIZE=2 FACE="Arial">reference current which for an LM317 is 50 to 100 µA, plus the swamping</FONT>
<BR><FONT SIZE=2 FACE="Arial">current which is usually at least 1 mA.&nbsp; You *can* therefore use an</FONT>
<BR><FONT SIZE=2 FACE="Arial">LM317 for as little as 1 mA with some limitation on accuracy.</FONT>
</P>

<P><FONT SIZE=2 FACE="Arial">&nbsp; I'm sure the LM317 has a far higher power dissipation than the CRDs.</FONT>
</P>
</UL>
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Surely by defination the dissipation would be the same?&nbsp; To deliver a set current (Y amps) given a supply voltage and a load resistance, the device has to drop X volts.&nbsp; Whatever device you use, as long as it's a two terminal device and therefore current in=current out, the dissipation will be the same; XY watts.&nbsp; Have I missed something obvious here?</FONT></P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Mike Rigby-Jones</FONT>
</P>

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1999\12\03@113246 by Dave Minkler

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Look at 1N5283 through 1N5314.  Field effect current regulator diodes
with currents ranging from about 0.2mA to 4.2mA

Regards,
mink

1999\12\03@135022 by William Chops Westfield

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   I am surprised that these CRD devices do not see more wide spread use.

Well, most electronics these days includes regulated voltages, which means
the CRD has to compete with a sub-$0.01 resistor...

BillW

1999\12\03@150644 by Alice Campbell

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Hi Harold,

i have this sitting on the whiteboard at the kitchen table right now,
hooked up to a solar cell

alice.

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I have used this to power a white LED nicely.

Attached is one of the original messages containing the circuit to
which you refer, with the correct ASCII art. (If you are using a fixed
point font, of course...)

Dan

On Mon, 8 Nov 1999 00:08:00 PST, Alice Campbell wrote:

{Quote hidden}

1999\12\04@164815 by paulb

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Michael Rigby-Jones wrote:

>> I'm sure the LM317 has a far higher power dissipation than the CRDs.
> Surely by defination the dissipation would be the same?

 "Power Dissipation" is a reference to the amount of power the
component is *capable* of safely handling, rather than the amount it
handles in any given circuit.

 The LM317 is designed to dissipate a watt or two without a heatsink,
20W with heatsink for the TO-220 package.  I'd suspect the CRDs are
rated about 0.5W or less.
--
 Cheers,
       Paul B.

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