simple 150uA constant current supply

[[email protected]]

---
Hey, asshole, _you're_ the one who wrote the spec, so don't blame your
stupidity or carelessness on someone else.

JF- Hide quoted text -

- Show quoted text -

86 replies on how to light an LED? Are these the big boys I am
supposed to be looking for - LOL!

 

[John Devereux]

What the hell is "hand balling?" Or do we really want to know that...

Apparently, "Handballing is a true expression of boy-love"



http://www.urbandictionary.com/define.php?term=handballing

 

[John Devereux]

Sorry, but nobody said anything about the eye or visible light, but thanks
anyway.


No, not hiding. Just a convenient spam harvester trap which inconveniences
the owners of such sites as well.
Are you objecting to the second use John?

As a rule, yes.

Also it will have the effect of increasing visibility of the site,
pushing up its ranking in google etc.

 

[Phil Allison]

"John Fields"

I think Phil was pretty close on his assessment this time.

** Dave has still not said what colour LED he has.

Makes a big difference....



....... Phil

 

[Rich Grise]

86 replies on how to light an LED? Are these the big boys I am
supposed to be looking for - LOL!

Everybody around here is tired of fielding beginner-level questions
that should already have been answered in the text, or asked at
sci.electronics.basics; and nobody likes googlies.

Good Luck!
Rich

 

[Dave]

ermm.....nope.

Don't think so IDIOT.
Didn't anyone ever tell you that there is more than one Dave in the
world...bwahahaha, how embarrasing is that!

Maybe no one else picked up on it, but I thought that kinda made you
look like a dick and, so far, you've been proving me right.

Most of the other guys won't mess with that kind of crap, but I love
beating up on you bullies and showing you up for the mean, vindictive
spirits you really are.

Wow, what a hilarious outcome to my original (polite) request for some
assistance.
You state you love beating people up and making them look like dicks.
This sounds to most rational people like you are the bully Fields and a very
damaged one too.

Face the mirror John...not nice is it?

I don't need to badmouth you.
I will just copy them the copious amount of vile abuse you have spewed out
over the many years...much simpler.
Then you will have lots more time to vent your angry, repressed self on the
group - it's ok John I won't tell anyone about, well, that stuff.

Dave

 

[MooseFET]

Thanks Martin but, it's not homework, I don't have any space for an
IC and this is battery powered. I can only spare about 30uA to
'generate' this supply.
There are microscopic nanopower opamps from Linear and others. Since all
you want is nominal +/-20% , and this is the same as Vbatt ranging from
2-3V, then something simple that does not require much battery current
would be like so, total bias around 16ua, compliance should be to within
a few hundred millivolts of the rail, and you could do even better with
a PFET:
View in a fixed-width font such as Courier.
.
.
.
. BATT---+-----------+-----------.
. | | |
. | | |
. [3.9k] | [390]
. | | |
. | .----|-----------+
. | | | |
. | | |\ | |
. | '-|-\| |<
. | | >---------| 2N3904
. +--------|+/| |\
. | |/ | |
. | | |
. | | Iout
. | |
. [166k] |
. | |
. | |
. COM---+-----------+-------
.
.
.
That circuit will usually oscillate, sometimes at two different
frequencies simultaneously.

Not if you use a really-really slow op-amp. The real part of the Zout
of the op amp will be high enough to prevent the 2N3904 from tuning up
and the 2N3904 is so fast compared to the op-amp that it adds no
noticable phase shift.

If you are using a non-really slow op-amp:
Modified version:

.
.
.
. BATT---+-----------+-----------.
. | | |
. | | |
. [3.9k] | [390]
. | | |
. | .----|--+--[R]---+
. | | | ! |
. | | |\ | [C] |
. | '-|-\| ! |<
. | | >--+-[R]--| 2N3904
. +--------|+/| |\
. | |/ | |
. | | |
. | | Iout
. | |
. [166k] |
. | |
. | |
. COM---+-----------+-------
.

Now add a ferrite bead in the collector. That doesn't affect the
oscillation situation much, but it does improve the
constantness-of-the-current at higher frequencies.

And bypass the 3.9K, for Pete's sake.

If it is a micro power op-amp, the bypass does little to help. The
internal compensation workings of the op-amp make the PSRR to the
minus rail so bad that the bypass on the 3.9K doesn't gain much.

 

[MooseFET]

If you are using a non-really slow op-amp:
Modified version:

.
.
.
. BATT---+-----------+-----------.
. | | |
. | | |
. [3.9k] | [390]
. | | |
. | .----|--+--[R]---+
. | | | ! |
. | | |\ | [C] |
. | '-|-\| ! |<
. | | >--+-[R]--| 2N3904
. +--------|+/| |\
. | |/ | |
. | | |
. | | Iout
. | |
. [166k] |
. | |
. | |
. COM---+-----------+-------
.

The modern offsets are low enough to make something like this work too:
View in a fixed-width font such as Courier.

.
.
.
. BATT---+-------------+-----------.
. | | |
. | | |
. [3.3k] | [330]
. | | |
. +--[330]-+----|---[3.3k]--+
. | | | |
. | | |\ | |
. | '-|-\| |<
. | | >---[33]--| 2N3904
. +----------|+/| |\
. | |/ | |
. | | |
. | | Iout
. | |
. [166k] |
. | |
. | |
. COM---+-------------+-------
.
.
.

How about this for a crappy circuit:

Dambit! my cursor just went away so I describe not ascii art the
circuit
Assume a micor power rail to rail op-amp.

If the minus rail of the op-amp goes to the load, there is a resistor
in the plus rail and the inverting input and output are also hooked to
the plus rail, you get a truly awful constant current source.

The opamp's output will pull down on the resistor sinking current to
the load on the minus power.

 

[krw]

He is a total retard. His very first statement is ambiguous, at best.
He states "150uA which will be around 2V". I don't think this dope knows
ANY electronics to be that far off the mark.


LEDs typically top out at 150mA, not micro-amps.

This LED should probably run at 20mA.

150µA probably won't illuminate it at all.

A couple of weeks ago, we characterized a bunch of neato Osram
surface-mount right-angle leds. "Bright" was in the ballpark of 5-10
mA, depending on color, and "dim" [1] was 0.5 to 1 mA. One of them was
just barely visible, in office light, at 2 uA.

John

[1] surely you're familiar with the term "dim."

Nice!

 

[legg]

You'd be best to simply ignore inflamatory traffic on the net. It
seves no useful purpose.

What kind of LED are you working with and would an LM10BL with one
sensing resistor work for you? The reference is 200mV and supply
current ~300uA.

Others might have ideas for low current, low voltage references that
might complement the tlv2760's 20uA supply current.

RL

 

[legg]

I found an LT6650 that combines a 400 mV reference and an op-amp with a
supply current of 5.6 uA typical, in a 5 lead SOT23 package. I made a
SwitcherCad simulation, with one 2.7 kOhm resistor, that holds LED current
to 148.524 uA (exactly), from 2.2 volts to 5 volts. Even better, it draws
only 17.75 uA from the battery, so you get an efficiency of 770%. Yes, 39
uW in and 300 uW out. There must be an error in the model, but I think it
will run on 170 uA. Of course the LT6650 costs $1.88, but *what a deal* for
an "over unity" part!

This has been an interesting thread, whether or not it has helped the OP.
The designs offered are useful in general, and I've learned a few things.

Paul

Top marks.

RL

 

[legg]

[1] surely you're familiar with the term "dim."

Nice!

I have taken measurements that are almost identical. The first LED video
screen I worked on had a circuit that measured the LED forward voltage.
The way it was configured pumped 1uA into the LEDs, and was (barely)
visible. It turned out to be easier for me to measure sub-microamp
"leakage" currents with a vacuum cleaner. We had bugger all test gear
(almost everything I used I was renting to the company), and the "nook &
cranny cleaning" pipe from the end of the vacuum cleaner was thick black
plastic that tapered down to a narrow slot; black tape made it narrower
still. By placing it over a led with my eye firmly over the other end, I
could see well below 1uA.

the problem turned out to be easy to fix, and was inherent on the design
of the voltage sensing circuit (not mine), which I duly modified. 3
years later I left, and the guy who designed the original circuit
changed it back the next PCB revision (he never did like me). Funnily
enough, they had a huge problem with contrast (black isnt very black
when all the LEDs are glowing faintly), and had to do another PCB
respin. He didnt use my exact fix, rather its dual, which ended up being
more expensive. pants-wettingly funny. That firm made all their
technical staff redundant this year (including him), and no longer build
anything.

Let me guess - they went onto fabless dsp-intensive AV controllers....
with a new crop of wonder boys, known to the new venture capitalists.

RL

 

[Paul E. Schoen]

I found an LT6650 that combines a 400 mV reference and an op-amp with a
supply current of 5.6 uA typical, in a 5 lead SOT23 package. I made a
SwitcherCad simulation, with one 2.7 kOhm resistor, that holds LED
current to 148.524 uA (exactly), from 2.2 volts to 5 volts. Even better,
it draws only 17.75 uA from the battery, so you get an efficiency of
770%. Yes, 39 uW in and 300 uW out. There must be an error in the model,
but I think it will run on 170 uA. Of course the LT6650 costs $1.88, but
*what a deal* for an "over unity" part!

This has been an interesting thread, whether or not it has helped the
OP. The designs offered are useful in general, and I've learned a few
things.

Paul

=====================================================================================

That's okay but you would want to buy yourself a bit more headroom with
something like this:
View in a fixed-width font such as
Courier.

.
.
.
.
.
. LTC6650
.
. |\
. -----|+\ ~~
. | | >-+----+--|>|--.
. 400mV .-|-/ | | |
. | | |/ === [110k] |
. | | 1u| | |
. --- | | | |
. '------|----+-[22k]-+
. | |
. | [300]
. | |
. --- ---

Yes, that could be done if you really needed it to work below 2.2 volts
supply. But comes at the expense of more parts, less efficiency, and not
quite as good current regulation if the diode Vf varies due to temperature,
production lot, aging, etc. The battery is probably just about shot at 2.2
volts, and a gradual dimming might be a "good thing".

I didn't notice the requirement for the 1 uF capacitor. Thanks for pointing
that out. Now the simulation shows a little start-up oscillation, but the
model is still flawed, since I am still drawing only 18 uA from the supply
for 150 uA output. And it's not April 1 anymore.

Paul

================================================================================

Version 4
SHEET 1 880 680
WIRE 112 144 -80 144
WIRE 112 208 112 144
WIRE -80 224 -80 144
WIRE 256 256 224 256
WIRE 320 256 256 256
WIRE 384 320 384 256
WIRE 384 320 224 320
WIRE 384 336 384 320
WIRE 256 352 256 256
WIRE -80 416 -80 304
WIRE 112 416 112 368
WIRE 112 416 -80 416
WIRE 256 416 112 416
WIRE 384 416 256 416
WIRE -80 464 -80 416
FLAG -80 464 0
SYMBOL SpecialFunctions\\LT6650 112 288 R0
SYMATTR InstName U1
SYMBOL voltage -80 208 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 132 Left 0
SYMATTR SpiceLine Rser=.1
SYMATTR InstName V1
SYMATTR Value 3
SYMBOL res 368 320 R0
SYMATTR InstName R1
SYMATTR Value 2.7k
SYMBOL LED 320 272 R270
WINDOW 0 72 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D1
SYMATTR Value QTLP690C
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap 240 352 R0
SYMATTR InstName C1
SYMATTR Value 1µ
SYMATTR SpiceLine V=16 Irms=1.816 Rser=0.031 MTBF=0 Lser=0 mfg="KEMET"
pn="C0805C105K4RAC" type="X7R" ppPkg=1
TEXT -112 504 Left 0 !.tran .05 startup

 

[Fred Bartoli]

Fred Bloggs a écrit :

Paul E. Schoen wrote:





What kind of LED are you working with and would an LM10BL with one
sensing resistor work for you? The reference is 200mV and supply
current ~300uA.

Others might have ideas for low current, low voltage references that
might complement the tlv2760's 20uA supply current.

RL


I found an LT6650 that combines a 400 mV reference and an op-amp
with a supply current of 5.6 uA typical, in a 5 lead SOT23 package.
I made a SwitcherCad simulation, with one 2.7 kOhm resistor, that
holds LED current to 148.524 uA (exactly), from 2.2 volts to 5
volts. Even better, it draws only 17.75 uA from the battery, so you
get an efficiency of 770%. Yes, 39 uW in and 300 uW out. There must
be an error in the model, but I think it will run on 170 uA. Of
course the LT6650 costs $1.88, but *what a deal* for an "over unity"
part!

This has been an interesting thread, whether or not it has helped
the OP. The designs offered are useful in general, and I've learned
a few things.

Paul

=====================================================================================


That's okay but you would want to buy yourself a bit more headroom
with something like this:
View in a fixed-width font such as
Courier.

.
.
.
.
.
. LTC6650
.
. |\
. -----|+\ ~~
. | | >-+----+--|>|--.
. 400mV .-|-/ | | |
. | | |/ === [110k] |
. | | 1u| | |
. --- | | | |
. '------|----+-[22k]-+
. | |
. | [300]
. | |
. --- ---

Yes, that could be done if you really needed it to work below 2.2
volts supply. But comes at the expense of more parts, less efficiency,
and not quite as good current regulation if the diode Vf varies due to
temperature, production lot, aging, etc. The battery is probably just
about shot at 2.2 volts, and a gradual dimming might be a "good thing".

I don't know that a simple LED indicator drive requires all that expense
and precision. You're the one who went with a $2 versus a $0.45 part. I
don't see that it's justified unless something else in the product
requires a reference. I did jump the gun on the first circuit,
absolutely terrible dI/dV, unusable actually. Taking the
self-referential opamp circuit as a minimum acceptable performance, with
dI/dV=-I/V, the reference circuit meets it with overheads, VOH, in
excess of Vref/2. This gets you good-enough regulation down to 2V, and
you have a reference you can tap into if necessary.
View in a fixed-width font such as Courier.

.
.
.
.
.
.
.
. |\ V
. .-----|+\ + - Vref-VOH
. | | >---+---|>|----. k= --------
. Vref .-|-/ | ~ | V
. | | |/ [R1] || I
. | | | |v
. | | | | dI I Vref-VOH
. | '--------+--[R2]----+ + -- = - - * --------
. | + - | dV V VOH
. | kV [Rcs] VOH
. | | -
. '-----------------------' > Vref
. => VOH = ----
. 2
. LT6650
.
. |\ V
. .-----|+\ + -
. | | >---+---|>|----.
. 400mV .-|-/ | ~ |
. | | |/ [120k] || I k=0.1
. | | | |v
. | | | |
. | '--------+--[13k]---+ +
. | + - |
. | kV [1.2k] 200mV
. | | -
. '-----------------------'
.
.

I didn't notice the requirement for the 1 uF capacitor. Thanks for
pointing that out. Now the simulation shows a little start-up
oscillation, but the model is still flawed, since I am still drawing
only 18 uA from the supply for 150 uA output. And it's not April 1
anymore.

I don't know that the 1u is necessary unless there is capacitive loading
somewhere, the amp is unity gain stable, and they seem to go to great
lengths to filter the power supply because the PSRR is *real* bad on
that part...

Paul

I've not seen the whole thread, so...

You don't need the ref source and get Vbatt independence by using the
LED as the ref voltage.

___ ___
.-|___|---+---|___|--.
| | |
=== | |\| |
GND '-|-\ |
| >-----+
.-|+/ |
| |/| .-.
| === | |
| GND | |
| '-' (*)
| | ___
'----------+----|___|--- +V
| NC
V ->
-
|
===
GND


(*) using a GND supplied opamp with a bipolar output stage ensures
startup, or add this resistor.

 

[MooseFET]

Fred Bloggs a écrit :

Paul E. Schoen wrote:

What kind of LED are you working with and would an LM10BL with one
sensing resistor work for you? The reference is 200mV and supply
current ~300uA.
Others might have ideas for low current, low voltage references that
might complement the tlv2760's 20uA supply current.
RL
I found an LT6650 that combines a 400 mV reference and an op-amp
with a supply current of 5.6 uA typical, in a 5 lead SOT23 package.
I made a SwitcherCad simulation, with one 2.7 kOhm resistor, that
holds LED current to 148.524 uA (exactly), from 2.2 volts to 5
volts. Even better, it draws only 17.75 uA from the battery, so you
get an efficiency of 770%. Yes, 39 uW in and 300 uW out. There must
be an error in the model, but I think it will run on 170 uA. Of
course the LT6650 costs $1.88, but *what a deal* for an "over unity"
part!
This has been an interesting thread, whether or not it has helped
the OP. The designs offered are useful in general, and I've learned
a few things.
Paul
=====================================================================================
That's okay but you would want to buy yourself a bit more headroom
with something like this:
View in a fixed-width font such as
Courier.
.
.
.
.
.
. LTC6650
.
. |\
. -----|+\ ~~
. | | >-+----+--|>|--.
. 400mV .-|-/ | | |
. | | |/ === [110k] |
. | | 1u| | |
. --- | | | |
. '------|----+-[22k]-+
. | |
. | [300]
. | |
. --- ---
Yes, that could be done if you really needed it to work below 2.2
volts supply. But comes at the expense of more parts, less efficiency,
and not quite as good current regulation if the diode Vf varies due to
temperature, production lot, aging, etc. The battery is probably just
about shot at 2.2 volts, and a gradual dimming might be a "good thing".

I don't know that a simple LED indicator drive requires all that expense
and precision. You're the one who went with a $2 versus a $0.45 part. I
don't see that it's justified unless something else in the product
requires a reference. I did jump the gun on the first circuit,
absolutely terrible dI/dV, unusable actually. Taking the
self-referential opamp circuit as a minimum acceptable performance, with
dI/dV=-I/V, the reference circuit meets it with overheads, VOH, in
excess of Vref/2. This gets you good-enough regulation down to 2V, and
you have a reference you can tap into if necessary.
View in a fixed-width font such as Courier.

.
.
.
.
.
.
.
. |\ V
. .-----|+\ + - Vref-VOH
. | | >---+---|>|----. k= --------
. Vref .-|-/ | ~ | V
. | | |/ [R1] || I
. | | | |v
. | | | | dI I Vref-VOH
. | '--------+--[R2]----+ + -- = - - * --------
. | + - | dV V VOH
. | kV [Rcs] VOH
. | | -
. '-----------------------' > Vref
. => VOH = ----
. 2
. LT6650
.
. |\ V
. .-----|+\ + -
. | | >---+---|>|----.
. 400mV .-|-/ | ~ |
. | | |/ [120k] || I k=0.1
. | | | |v
. | | | |
. | '--------+--[13k]---+ +
. | + - |
. | kV [1.2k] 200mV
. | | -
. '-----------------------'
.
.

I didn't notice the requirement for the 1 uF capacitor. Thanks for
pointing that out. Now the simulation shows a little start-up
oscillation, but the model is still flawed, since I am still drawing
only 18 uA from the supply for 150 uA output. And it's not April 1
anymore.

I don't know that the 1u is necessary unless there is capacitive loading
somewhere, the amp is unity gain stable, and they seem to go to great
lengths to filter the power supply because the PSRR is *real* bad on
that part...

I've not seen the whole thread, so...

You don't need the ref source and get Vbatt independence by using the
LED as the ref voltage.

___ ___
.-|___|---+---|___|--.
| | |
=== | |\| |
GND '-|-\ |
| >-----+
.-|+/ |
| |/| .-.
| === | |
| GND | |
| '-' (*)
| | ___
'----------+----|___|--- +V
| NC
V ->
-
|
===
GND

The LT6003 seems to be happy with no bypass capacitor even though
Linear doesn't seem to think so.

You can also flip the circuit around so that the LED's anode is at
Vcc. This would let you use a "single supply" op-amp.


Or perhaps with higher battery voltage:
(Modified version)

___ ___
.-|___|---+---|___|--.
| | |
=== | |\| |
GND '-|-\ |
| >-----+
.-|+/ |
| |/| .-.
| ! | !
| ! | |
| ! '-'
| ! |
'---+------+
|
V ->
-
|
===
GND

Many R-R input op-amps still work if the inverting input is pulled
below ground while the non-inverting input is at ground. This circuit
uses the op-amps idle current to ensure starting. The down side is
that the op-amp needs to be a very low voltage one.

 

[Paul E. Schoen]

Right, we covered that earlier, and have been calling it the
self-referential circuit. That is the one with dI/dV=-I/V , I and V are
for the LED. The OA was a micropower type.

I made a self-referential circuit using a 2N3904 and 2N3906. It works in
the SwitcherCad simulator down to 2.1 volts. It may not be very stable with
temperature, but it's cheap and easy.

Paul

===========================================================================

Version 4
SHEET 1 1172 680
WIRE -16 0 -256 0
WIRE 80 0 -16 0
WIRE -16 32 -16 0
WIRE 160 80 80 80
WIRE 80 96 80 80
WIRE 160 112 160 80
WIRE -16 144 -16 112
WIRE 16 144 -16 144
WIRE -256 176 -256 0
WIRE -16 208 -16 144
WIRE 80 224 80 192
WIRE 160 224 160 192
WIRE 160 224 80 224
WIRE 80 256 80 224
WIRE 80 256 48 256
WIRE -16 320 -16 304
WIRE 80 320 80 256
WIRE -256 416 -256 256
WIRE -16 416 -16 400
WIRE -16 416 -256 416
WIRE 48 416 -16 416
WIRE 80 416 80 384
WIRE 80 416 48 416
WIRE 48 432 48 416
FLAG 48 432 0
SYMBOL pnp 16 192 M180
WINDOW 0 49 26 Left 0
WINDOW 3 38 52 Left 0
SYMATTR InstName Q2
SYMATTR Value 2N3906
SYMBOL res 0 416 R180
WINDOW 0 36 76 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName R1
SYMATTR Value 50k
SYMBOL res 64 -16 R0
SYMATTR InstName R5
SYMATTR Value 1.5k
SYMBOL voltage -256 160 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 3
SYMBOL npn 48 208 M0
SYMATTR InstName Q3
SYMATTR Value 2N3904
SYMBOL LED 64 320 R0
WINDOW 3 23 71 Left 0
SYMATTR InstName D1
SYMATTR Value QTLP690C
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res -32 16 R0
SYMATTR InstName R2
SYMATTR Value 40k
SYMBOL res 144 96 R0
SYMATTR InstName R3
SYMATTR Value 4.7Meg
TEXT -224 440 Left 0 !.tran 1m startup

 

[James Arthur]

I made a self-referential circuit using a 2N3904 and 2N3906. It works in
the SwitcherCad simulator down to 2.1 volts. It may not be very stable with
temperature, but it's cheap and easy.

Paul

[snip SWCIII ckt]

For improved temp. stability just compensate Q2's Vbe:

Vcc
-+-
|
+------------.
| |
[D2] [1.5k]
| |
[68k] +---.
| |<' |
+---------| [4.7M]
| Q2 |\ |
| +----'
| |
\| Q1 |
|---------+
.<| |
| [LED]
[150k] |
| ===
===

(D2 added, resistor values adjusted.)

Try it and compare![*]


[*] In SWCIII, .STEP TEMP 0 50 10


Cheers,
James Arthur

 

[Paul E. Schoen]

I made a self-referential circuit using a 2N3904 and 2N3906. It works in
the SwitcherCad simulator down to 2.1 volts. It may not be very stable
with
temperature, but it's cheap and easy.

Paul

[snip SWCIII ckt]

For improved temp. stability just compensate Q2's Vbe:

Vcc
-+-
|
+------------.
| |
[D2] [1.5k]
| |
[68k] +---.
| |<' |
+---------| [4.7M]
| Q2 |\ |
| +----'
| |
\| Q1 |
|---------+
.<| |
| [LED]
[150k] |
| ===
===

(D2 added, resistor values adjusted.)

Try it and compare![*]


[*] In SWCIII, .STEP TEMP 0 50 10


Cheers,
James Arthur

That is much better, about 0.48%/Degree C. I didn't know about the .STEP
directive. This info may come in handy. I think the OP has left the
building, but I have gained useful information.

Thanks!

Paul

 

[James Arthur]

[snip SWCIII ckt]

For improved temp. stability just compensate Q2's Vbe:

Vcc
-+-
|
+------------.
| |
[D2] [1.5k]
| |
[68k] +---.
| |<' |
+---------| [4.7M]
| Q2 |\ |
| +----'
| |
\| Q1 |
|---------+
.<| |
| [LED]
[150k] |
| ===
===

(D2 added, resistor values adjusted.)

Try it and compare![*]

[*] In SWCIII, .STEP TEMP 0 50 10

Cheers,
James Arthur

That is much better, about 0.48%/Degree C. I didn't know about the .STEP
directive. This info may come in handy.

I think the OP has left the
building, but I have gained useful information.

OP? Runnt oft by the ruckus, I 'spect. But we can still have fun,
can't we?

Cheers,
James Arthur

 

[Hattori Hanzo]

On Apr 4, 2:26 pm, "Paul E. Schoen" <[email protected]> wrote:

I made a self-referential circuit using a 2N3904 and 2N3906. It works in
the SwitcherCad simulator down to 2.1 volts. It may not be very stable
with
temperature, but it's cheap and easy.

Paul

[snip SWCIII ckt]

For improved temp. stability just compensate Q2's Vbe:

Vcc
-+-
|
+------------.
| |
[D2] [1.5k]
| |
[68k] +---.
| |<' |
+---------| [4.7M]
| Q2 |\ |
| +----'
| |
\| Q1 |
|---------+
.<| |
| [LED]
[150k] |
| ===
===

(D2 added, resistor values adjusted.)

Try it and compare![*]

[*] In SWCIII, .STEP TEMP 0 50 10

Cheers,
James Arthur

That is much better, about 0.48%/Degree C. I didn't know about the .STEP
directive. This info may come in handy.

I think the OP has left the
building, but I have gained useful information.

OP? Runnt oft by the ruckus, I 'spect. But we can still have fun,
can't we?

Cheers,
James Arthur

A ruckus of his making.