Driver to drive?

[Baron]

John Larkin wrote:

On Tue, 05 May 2009 00:13:51 +1000, Bob Larter <bobbylarter@gmail.com
wrote:

John Larkin wrote:
On Mon, 04 May 2009 17:47:29 +1000, Bob Larter
bobbylarter@gmail.com> wrote:

Eeyore wrote:
John Larkin wrote:
[...]
Here's the box:

ftp://jjlarkin.lmi.net/99A260A1.JPG

ftp://jjlarkin.lmi.net/99A260A3.JPG

ftp://jjlarkin.lmi.net/99S260A.JPG

Seems to work now.
Ah ! Point to point wiring. The toob nuts would be proud of you.
;~)
Well, that's one way to reduce leakage!

This circuit has only one really leakage-sensitive node, and it's
not on the terminal strip. Its insulation is mostly air. The only
leakage is on the body of the opamp (National claims 10 fA typ) and
the polycarb thing I added to the front panel.

Unfortunately, on the LMC6001 the ni input is pin 3, and pin 4 is
-5V.

With the kinds of currents you're measuring, I'd be worrying about
skin oil from your fingers on the chip package, terminals, etc. It
might be worth your while to brush everything down with isopropyl
alcohol.

The opamp is as clean as I can get it. With better measurement
technique and zeroing out the offset of the opamp (only about 100 uV)
I'm seeing about 30 fA error now.

Hey, I could slip a few mylar shims under the polycarb insulator, lift
it up a hair, and increase the leakage distance of the middle
terminals to the chassis.

John

You could tape a bag of silica gel in there ! You would need to make
the compartment air tight though.

--
Best Regards:
Baron.

 

[Joerg]

Rich Grise wrote:

On Mon, 04 May 2009 09:41:17 -0700, Joerg wrote:

Jasen Betts wrote:
On 2009-05-03, Joerg <notthisjoergsch@removethispacbell.net> wrote:
RFI-EMI-GUY wrote:
In my house attic, I have several 4 inch white PVC vent stacks which are
simply white PVC drain pipe extending from the wall headers through the
attic and the roof. On the roof, these are covered with lead flashing to
prevent water from getting inside the house. I have been doing a lot of
work in the attic, and have noticed that these pipes "glow" quite
noticeably as a result of the sunlight outside. As this often happens
when the sun is at the horizon and thus at an angle below which direct
coupling into the pipe would be possible, I am very curious as to the
reason that the visible infrared portion is so much more visible than
white light spectrum. Has anyone else noticed this? What is going on?

White PVC sticking out the roof? 4"? Wow. White PVC usually becomes
rotten from UV pretty quickly. If it isn't painted it begins to turn
brown within 2-3 years in our area. After some more years you can
sometimes crumble it by hand.
if it's loaded with TiO it'll last several decades exposed.

Contractors typically use the cheapest stuff they can get. Made in China.

So, how is Chinese PVC different from "domestic" PVC (if there is any such
thing any more)? I'd have assumed that PVC is PVC.

AFAIK there is stuff mixed in to provide UV stabilization and so on. We
have some 10ft lengths of very old PVC pipe, plus elbows and whatnot in
the garage from the previous owner of the house. Wherever I used some of
that it took forever to blacken or never blackend. Sometimes you end up
with two tees in a row, same location. After 2-3 years one is
brownish-black, the other almost as white as new. Guess which one is the
new tee?

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Baron]

Rich Grise wrote:

On Sun, 03 May 2009 17:58:21 -0700, John Larkin wrote:
On Sun, 3 May 2009 17:32:18 -0700 (PDT), Greegor
Greegor47@gmail.com
On May 3, 7:23 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
These crappy RatShack terminal posts are actually conductive!

http://www.radioshack.com/product/index.jsp?productId=2103639

A pair of them leak 12 pA to the chassis at +1 volt. If I ground
myself and hold the plastic screw part of one, it goes up to 20.

So I'll have to replace them with some Pomonas or something. What a
nuisance.

Pity; they do look nice.

John

0.000000012 Amp? LOL

I just finished machining a couple of big slots in the aluminum box,
where the critical binding posts go, and added a polycarb plate that
the terminal strips mount on. Now the leakage is showing about 100
fA, basically my measurement limit. It was ugly, machining the
already-"finished" electronics. I tried milling it dry, but that
didn't work, so I wound up getting chips and cutting fluid
everywhere. Had to clean all that up.

It's amazing what a few drops of Tapmatic will do.

Here's the box:

ftp://jjlarkin.lmi.net/99A260A1.JPG

ftp://jjlarkin.lmi.net/99A260A3.JPG

ftp://jjlarkin.lmi.net/99S260A.JPG

Seems to work now.

Geez, John, did you just fall off the turnip truck yesterday? I've
been doing this sort of thing for decades. For steel, practically any
ol' ordinay petroleum-based oil will work, and for aluminum lard,
which in Mexicanese is "manteca". It works like a charm, albeit, as
you've noticed, it makes mell of a hess, but you do get real purty
results.[1] ;-)

Cheers!
Rich
[1] yes, I know it should be "really pretty", but I thought the way
I wrote it here would be somehow more poetic, or amusing, or whatever.
;-)

I'd have just used a hole punch !

--
Best Regards:
Baron.

 

[Spehro Pefhany]

On Mon, 04 May 2009 19:23:23 GMT, Rich Grise <richgrise@example.net>
wrote:

On Mon, 04 May 2009 09:41:17 -0700, Joerg wrote:

Jasen Betts wrote:
On 2009-05-03, Joerg <notthisjoergsch@removethispacbell.net> wrote:
RFI-EMI-GUY wrote:
In my house attic, I have several 4 inch white PVC vent stacks which are
simply white PVC drain pipe extending from the wall headers through the
attic and the roof. On the roof, these are covered with lead flashing to
prevent water from getting inside the house. I have been doing a lot of
work in the attic, and have noticed that these pipes "glow" quite
noticeably as a result of the sunlight outside. As this often happens
when the sun is at the horizon and thus at an angle below which direct
coupling into the pipe would be possible, I am very curious as to the
reason that the visible infrared portion is so much more visible than
white light spectrum. Has anyone else noticed this? What is going on?

White PVC sticking out the roof? 4"? Wow. White PVC usually becomes
rotten from UV pretty quickly. If it isn't painted it begins to turn
brown within 2-3 years in our area. After some more years you can
sometimes crumble it by hand.

if it's loaded with TiO it'll last several decades exposed.


Contractors typically use the cheapest stuff they can get. Made in China.

So, how is Chinese PVC different from "domestic" PVC (if there is any such
thing any more)? I'd have assumed that PVC is PVC.

Thanks,
Rich

Nah, there's virgin and there's regrind, and recycled plastic crap (in
varying percentages of each). There's LOTs of different additives, to
improve extrudability, placticizer to make it flexible, heat
stabilizers, UV stabilizers, fire retardants, etc.. Some years ago
Taiwan makers were making window blinds from extruded PVC with a lot
of UV stabilizer (as you might expect)-- only problem was that it was
lead, and the blinds slowly disintegrated under sunlight, yielding
lead-bearing dust. There's also potential health problems with some
fire retardants, which have been banned already in Europe and maybe in
North America too by now. Some of the smelly flexible PVC (like
swimming pool liner smell) is as much as 30% plasticizer chemicals.

But most PVC pipe, IME, is made domestically because it's cheaper to
turn the silos full of powder into bulky hollow tubing close to the
point of use, and requires virtually no labor (automated take-off
equipment, automated saws and stacking, and then straight onto the
flatbed).

 

[keithw86@gmail.com]

On May 4, 12:48 pm, alertj...@rediffmail.com wrote:

On May 4, 12:54 pm, "keith...@gmail.com" <keith...@gmail.com> wrote:



On May 4, 11:42 am, alertj...@rediffmail.com wrote:

On May 4, 8:58 am, "keith...@gmail.com" <keith...@gmail.com> wrote:

On May 4, 12:46 am, alertj...@rediffmail.com wrote:

Based on trends in mask and design costs for standard cells, vs. FGPA
capabilities, do
you believe the number of new designs per year executed in standard
cells will increase
or decrease in the future as compared with a baseline of 2007 ?

I think it will increase, what do you think ?

I think you're nuts, but you can ignore history at your peril.

Dave..You are smart..It was an exam question. But I am not convinced
by the answer professor gave me...that FPGAs will takeoverstandard> celldesigns thereby reducing the number ofstandard celldesigns. I
think as the performance and power of FPGAs will be bad compared to SC
designs, SC designs are always going to be winners
and I dont think FPGAs will take over.

You didn't answer Dave.

FPGAs won't "take over"standard celldesigns any more than digital
esigns will "take over" analog designs or microcontrollers will "take
over" logic designs.  Each has its purpose and the lines will shift.

Standard cells will certainly continue to lose designs to FPGAs as
costs rise.  There will continue to be a niche forstandard cell, as
well as custom logic, for those applications that can afford the costs
(where "afford" == require).

Keith,
I agree that Standard Cells will continue to lose designs to FPGA as
FPGA costs keeps coming down and can hold bigger designs in them.
But, won't the performance/power requirements becomes more and more
stringent when we move into future ? Excuse me for using the term
"take over", displace would be more appropriate.

FPGA costs coming down isn't nearly as important as their performance
going up and cost of standard cell designs. Yes, there will always be
niches for standard cells, though increasingly small. The number of
these applications will be bounded by the astronomical costs
involved. Because the costs can be spread around more ASSPs will be
far more prevalent, further eroding the ASIC market.

BTW, not all FPGAs are Xilinx' power hogs. ;-)

 

[James Rollins]

On May 4, 8:47 am, MooseFET <kensm...@rahul.net> wrote:

On May 3, 4:09 pm, James Rollins <james.rolli...@gmail.com> wrote:

In my never ending quest for a cheap and simple high voltage
regulation I have come up with a simple dual capacitor mode. This is
similar to a Buck circuit without the inductor.

http://i41.tinypic.com/68zl03.jpg

That circuit is about as efficient as a linear regulator.

No so. A linear regulator must drop the full voltage difference. The
capacitor resistors are only there to reduce the charging rate on the
capacitor so that the fet switching times are within spec. Ideally no
capacitor resistance would be needed and the capacitors would charge
up to the programmed voltage instantaneously and the switches would
cut the capacitor off at the programmed voltage. The capacitor
resistors are not analogous to the bjt in a linear regulator. In they
behave very differently in what they are doing. The bjt acts as a
current controlled resistance while the capacitor resistors are only
reducing the charging times and effect the duty cycle. It's a
different story for large loads but in this case for loads larger than
100kohms they are not even close to being the same.

[....]

My requirements is a programmable constant voltage supply from around
0 voltages to 1kV driving a load of around 100kohms to 1Mohms. The
regulation should be less than 1% or better.

I have done a design that did that.  How much ripple can you stand?

Last line... 1%. Ideally 0.1% or even 0.01%.

If you make the basic flyback switcher and drive a transformer with
it, getting 300V on the secondary isn't hard.  A voltage tripler with
the two diodes in the flyback direction and a choke in series with the
diode in the forwards direction gives 1000V.

The reason to stay down at 300V is that I found a transformer that
could do that.

I only need to reduce the voltage rather than increase it. I have a
main power supply that will give the 1000V and I need to reduce this
subcircuits that will use some fraction of the mains. The circuit I'm
using is simply a variation of a buck circuit taking into account the
low loads I'm driving. It replaces the inductor with a resistor and
prevents the voltage dividing effect when the load is connected
directly to the power supply which the inductor would take care of
naturally. In fact I might eventually end up going with a buck circuit
if I can find decent low cost inductors to get the regulation I need.
I just found that the circuit above, at least ideally, seems to give
me great regulation that I don't think I can get with the standard
buck.

In case your interested:

The charging phase of one capacitor is

Vc(t) = (V - Vc0)*(1 - e^(-t/Rc/C)) + Vc0
t_charge = -Rc*C*ln((V-Vc)/(V - Vc0))

The discharging phase is

Vc(t) = Vc0*e^(-t/R/C)
t_discharge = - R*C*ln(Vc/Vc0)

t_charge and t_discharge basically determine the duty cycle and
frequency but also regulate the rise/fall times of the fet. One can
reduce Rc but this reduces the efficiency of the fets and potentially
decreases the regulation. Alternatively it could be balanced out by
using a higher capacitance. t_charge must obviously be smaller than
t_discharge. For ideal switches t_charge can simply be chosen to be 0
and hence it should be clear that it would be much more better than a
linear regulator.

Given

R = 10^5, Rc = 10^3, C = 10^(-5), V = 1000, Vc = 100, Vc0 = 0.1%
within Vc then

t_charge ~= 1us
t_discharge ~= 1ms

That is, it takes 1us to charge the capacitor and 1ms to discharge it.
Taking the rise and fall time to be 1/100th of this time requires a
rise/fall time of ~ 10ns. Increasing the capacitance to 100uF reduces
this requirement by a factor of 10 as does increasing Rc by a factor
of 10.

 

[Jon Kirwan]

On Sun, 3 May 2009 21:21:54 -0700 (PDT), mj <elucify@gmail.com> wrote:

snip
To try to get a bright enough flash, I got some 0.5W white LEDs that
can take a max DC forward current of 150 mA, and have about a ~3.6
forward drop, producing an intensity of 130k mcd. (Not too clear on
the mcd part.) And dem suckers is bright when you're pumping even 100
mA through them. Like squint-to-look-at-it bright. They're in a
standard 5mm package (T-1 3/4, what is up with that package name?),
though it's sturdier than most you've probably seen. The LED looks
like it's been lifting weights, and the leads are shorter and fatter.

Anyway, I have two 2n2222's hooked up as a Darlington, with +5 Vcc,
driving the front Q's base with ~15mA (with a microcontroller pin).
There's NO current-limiting resistor on the back end, where the second
transistor's collector is attached to +5v, and the emitter goes
through the LED to ground.
snip

Some thoughts about the 2N2222. They probably can handle the pulses
of 1.5A for 200us and .4% duty (I am assuming, for now, that your
20-50 RPM is really 20 RPS = 200us/0.4%.) However, the Rc, Re, and Rb
plus the 26mV*(1+ln(1+I/Is)) are going to suggest something on the
order of 1.9 to 2.0 volts at the base. (I see Re=0.2, Rc=0.3, and
Rb=10 for one model I have, with a blind Is=1e-14, and I don't think
you can expect to get better than beta=30 here.)

Vbe = 26e-3*(1+ln(1+(1.5/30)/1e-14))+1.5*(.2+.3)+(10+.2)*(1.5/30)

Which reads out at about 2V.

Since this is a darlington, I'm assuming something like this:

|
about 2.7V | <--- about 2.2V
| ,--------+
v | |
R1 |/c Q2 |
ON----/\/\-----| 2N2222 |
|>e |
| |/c Q1
about 2V --> '------| 2N2222
|>e
|
|
gnd

That's Q1, I'm talking about. The Vbe of Q2 is about 0.7V and, if Q2
is considered saturated at about Vce=0.2V, I'd expect to see a Vce on
Q1 of 2.2V or so. [Note that Q2's base is about 0.5V above Q2's
collector, so that is going to conduct a little (.2V/60mV, about 3
orders, or maybe 0.1% of the base current -- nothing to get excited
about.)]

With a 5V source above, that leaves about 2.8V for your LED. Not the
3.6V you were talking about at 150mA. And you want 1500mA, not 150mA!
So your circuit probably won't get there.

Here's the same circuit with 150mA as the estimate:

|
about 1.45V | <--- about 1V
| ,--------+
v | |
R1 |/c Q2 |
ON----/\/\-----| 2N2222 |
|>e |
| |/c Q1
about 0.85V --> '------| 2N2222
|>e
|
|
gnd

This provides about 4V compliance (not sure if you are using a
resistor on the collector leg) for your LED. So at 150mA, it probably
has just about enough for your 3.6V requirement.

.....

All this suggests to me that you aren't going to see a lot more than
150mA. I don't have the LED model, but since it is white the LED is
blue with some phosphor used for the white appearances. Guessing a
simple model has me taking about 2.8V as the minimum on-voltage (which
I get from (700nm/400nm)*1.6V, extrapolating from a red led) and a
model where R=(3.6-2.8)/150mA or in the area of 5 ohms. Actually,
that seems too high to me, so that 2.8V estimate is probably wrong.
Let's assume it is closer to about 2 ohms or so (3.3V minimum.) At
1.5A, that's still 3V all by itself. Adding that to the 3.3V figure
gives you well more than 5V. So again, a problem even assuming your
darlington arrangement could support a Q1 Vce of 0V, which it cannot.

Your darlington arrangement creates one problem. Q1's Vce will be on
the order of 2V at those high currents and you don't have that kind of
headroom to spare. Your LED itself creates another. It's not likely
to allow 1.5A with only 5V of drive, under any circumstance. These
are guesses, admittedly. But what this seems to say is that you
probably need another voltage rail, at a minimum, if you want to get
up to 1.5A on your LED.

If you can live with less than that but still want a lot more than
150mA, the perhaps your LED will allow ... hmm ... say (4.4V-3.3V)/2
.... or about 500mA, let's call it, assuming you can limit your BJT
switch to a Vce of 0.6V or less. And no more than (4.8V-3.3V)/2 or
about 700mA. I think that's the best you can hope for. But I'd plan
no more than 500mA, after some testing first. In this case, you can
keep your rail, maybe, but you have to lose the darlington.

Jon

 

[James Rollins]

On May 4, 9:07 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On 4 May 2009 09:13:37 GMT, Jasen Betts <ja...@xnet.co.nz> wrote:



On 2009-05-04, James Rollins <james.rolli...@gmail.com> wrote:

You may as well use a single series fet+resistor, pwm controlled, and
one output cap. Or just use a linear regulator. All are about equally
efficient.

John

If you don't disconnect the load there will be a voltage spike and
also a voltage dividing effect. i.e., the load is connected to the
voltage source directly and depending on the ratio of the two
resistors the load will generally see a higher voltage than you might
want. Hence the reason why the load is disconnected. If the voltage
supply resistance is too small then it requires faster rise/fall times
to quickly stop charging the capacitor as it will end up charging up
much faster.

your circuit avoids neither of those problems.

The same problem still exists with your idea though. The fet's gate
will need to be held at a voltage that is within the source/drain of
usually around +-20V max.  But if the fet is sorta "floating" I am
unsure how to accomplish such a task. At least in a way that keeps
with the simplicity of the design.

I've thought about using a simple linear regulator idea but
unfortunately similar problems as well as other problems exist. Mainly
in this case the regulation seems much poorer and it is less
efficient. Although I'm not too interested in efficiency as I am
regulation. Trying to find cost effective HV bjt's is a bit of a
problem as compared to fets.

a linear series regulator is no less efficient than a series resistor for
dropping voltage, but it handles load fluctuations better.

you should do an energy audit on your design.

One of my products has a power switcher (variable output, 25 to 200
volts) using a series switching fet and a BIG power resistor feeding a
BIG output cap. A microprocessor/ADC checks the output voltage once
every millisecond and turns the fet on or off. Works great, and keeps
the room warm. It's about as efficient as a linear reg, but simpler,
and the heat's mostly in the resistor, not in the fet.

Sort of a delta-sigma regulator.

John

Similar to what I'm suggesting doing. I assume though your load is
very large compared to mine. At most I would be dissipating
1000^2/10^5 = 10W. I'm mainly doubling up so that when the fet is off
for one capacitor it is on for the other sot hat the load is never
disconnected from a capacitor as I need to supply it continuously. As
I mentioned one could probably do this just by adding a diode and
capacitor after the first capacitor so that it acts as a temporary
storage while the other capacitor is being charged.

How do you drive the gate of the fet with the uP?

 

[John Larkin]

On Mon, 4 May 2009 11:09:05 -0700 (PDT), James Rollins
<james.rollines@gmail.com> wrote:

On May 4, 9:07 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On 4 May 2009 09:13:37 GMT, Jasen Betts <ja...@xnet.co.nz> wrote:



On 2009-05-04, James Rollins <james.rolli...@gmail.com> wrote:

You may as well use a single series fet+resistor, pwm controlled, and
one output cap. Or just use a linear regulator. All are about equally
efficient.

John

If you don't disconnect the load there will be a voltage spike and
also a voltage dividing effect. i.e., the load is connected to the
voltage source directly and depending on the ratio of the two
resistors the load will generally see a higher voltage than you might
want. Hence the reason why the load is disconnected. If the voltage
supply resistance is too small then it requires faster rise/fall times
to quickly stop charging the capacitor as it will end up charging up
much faster.

your circuit avoids neither of those problems.

The same problem still exists with your idea though. The fet's gate
will need to be held at a voltage that is within the source/drain of
usually around +-20V max.  But if the fet is sorta "floating" I am
unsure how to accomplish such a task. At least in a way that keeps
with the simplicity of the design.

I've thought about using a simple linear regulator idea but
unfortunately similar problems as well as other problems exist. Mainly
in this case the regulation seems much poorer and it is less
efficient. Although I'm not too interested in efficiency as I am
regulation. Trying to find cost effective HV bjt's is a bit of a
problem as compared to fets.

a linear series regulator is no less efficient than a series resistor for
dropping voltage, but it handles load fluctuations better.

you should do an energy audit on your design.

One of my products has a power switcher (variable output, 25 to 200
volts) using a series switching fet and a BIG power resistor feeding a
BIG output cap. A microprocessor/ADC checks the output voltage once
every millisecond and turns the fet on or off. Works great, and keeps
the room warm. It's about as efficient as a linear reg, but simpler,
and the heat's mostly in the resistor, not in the fet.

Sort of a delta-sigma regulator.

John

Similar to what I'm suggesting doing. I assume though your load is
very large compared to mine. At most I would be dissipating
1000^2/10^5 = 10W. I'm mainly doubling up so that when the fet is off
for one capacitor it is on for the other sot hat the load is never
disconnected from a capacitor as I need to supply it continuously. As
I mentioned one could probably do this just by adding a diode and
capacitor after the first capacitor so that it acts as a temporary
storage while the other capacitor is being charged.

How do you drive the gate of the fet with the uP?

Optoisolator, with a small stock DC/DC converter to supply floating
power for the gate driver. The whole rig just precharges a capacitor
bank before we kick in the BIG power supply!

John

 

[Jan Panteltje]

On a sunny day (Mon, 4 May 2009 13:18:22 -0700 (PDT)) it happened mj
<elucify@gmail.com> wrote in
<4bb6d698-2dae-45a9-a583-c0500305a4a8@o20g2000vbh.googlegroups.com>:

'swhy I like I2C so much -- wiring up discrete chip select logic (not
to mention bus lines) is a PITA.

--mj

Yes, i2c is cool, I was one of the early adaptors...
Made the i2c external too, the i2c is cool as you can drive strings of logic
remotely from say a par port of a PC, while the task switching of the
OS has no effect, because basically i2c is static, and a delay makes no difference.
I had 50 units is a building with clock and sound all controlled by external i2c.
Designed and sold video equipment with i2c interface to PC running Linux too...
and I use it in my house for control.
For very long cables you need to draw up a driver

I have noticed the modern motherbourds still have a par port.. but no RS232...
So it is still very useful as interface to embedded too.

 

[Jon Kirwan]

On Mon, 4 May 2009 13:33:30 -0700 (PDT), mj <elucify@gmail.com> wrote:

On May 4, 4:07 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
On Sun, 3 May 2009 21:21:54 -0700 (PDT), mj <eluc...@gmail.com> wrote:
snip
To try to get a bright enough flash, I got some 0.5W white LEDs that
can take a max DC forward current of 150 mA, and have about a ~3.6
forward drop, producing an intensity of 130k mcd. (Not too clear on
the mcd part.) And dem suckers is bright when you're pumping even 100
mA through them. Like squint-to-look-at-it bright. They're in a
standard 5mm package (T-1 3/4, what is up with that package name?),
though it's sturdier than most you've probably seen. The LED looks
like it's been lifting weights, and the leads are shorter and fatter.

Anyway, I have two 2n2222's hooked up as a Darlington, with +5 Vcc,
driving the front Q's base with ~15mA (with a microcontroller pin).
There's NO current-limiting resistor on the back end, where the second
transistor's collector is attached to +5v, and the emitter goes
through the LED to ground.
snip

Some thoughts about the 2N2222.  They probably can handle the pulses
of 1.5A for 200us and .4% duty (I am assuming, for now, that your
20-50 RPM is really 20 RPS = 200us/0.4%.)  However, the Rc, Re, and Rb
plus the 26mV*(1+ln(1+I/Is)) are going to suggest something on the
order of 1.9 to 2.0 volts at the base.  (I see Re=0.2, Rc=0.3, and
Rb=10 for one model I have, with a blind Is=1e-14, and I don't think
you can expect to get better than beta=30 here.)

  Vbe = 26e-3*(1+ln(1+(1.5/30)/1e-14))+1.5*(.2+.3)+(10+.2)*(1.5/30)

Which reads out at about 2V.

Since this is a darlington, I'm assuming something like this:

                             |
      about 2.7V             | <--- about 2.2V
              |     ,--------+
              v     |        |
          R1      |/c Q2     |
   ON----/\/\-----|   2N2222 |
                  |>e        |
                    |      |/c Q1
       about 2V --> '------|   2N2222
                           |>e
                             |
                             |
                            gnd

That's Q1, I'm talking about.  The Vbe of Q2 is about 0.7V and, if Q2
is considered saturated at about Vce=0.2V, I'd expect to see a Vce on
Q1 of 2.2V or so.  [Note that Q2's base is about 0.5V above Q2's
collector, so that is going to conduct a little (.2V/60mV, about 3
orders, or maybe 0.1% of the base current -- nothing to get excited
about.)]

With a 5V source above, that leaves about 2.8V for your LED.  Not the
3.6V you were talking about at 150mA.  And you want 1500mA, not 150mA!
So your circuit probably won't get there.

Here's the same circuit with 150mA as the estimate:

                             |
      about 1.45V            | <--- about 1V
              |     ,--------+
              v     |        |
          R1      |/c Q2     |
   ON----/\/\-----|   2N2222 |
                  |>e        |
                    |      |/c Q1
    about 0.85V --> '------|   2N2222
                           |>e
                             |
                             |
                            gnd

This provides about 4V compliance (not sure if you are using a
resistor on the collector leg) for your LED.  So at 150mA, it probably
has just about enough for your 3.6V requirement.

....

All this suggests to me that you aren't going to see a lot more than
150mA.  I don't have the LED model, but since it is white the LED is
blue with some phosphor used for the white appearances.  Guessing a
simple model has me taking about 2.8V as the minimum on-voltage (which
I get from (700nm/400nm)*1.6V, extrapolating from a red led) and a
model where R=(3.6-2.8)/150mA or in the area of 5 ohms.  Actually,
that seems too high to me, so that 2.8V estimate is probably wrong.
Let's assume it is closer to about 2 ohms or so (3.3V minimum.)  At
1.5A, that's still 3V all by itself.  Adding that to the 3.3V figure
gives you well more than 5V.  So again, a problem even assuming your
darlington arrangement could support a Q1 Vce of 0V, which it cannot.

Your darlington arrangement creates one problem.  Q1's Vce will be on
the order of 2V at those high currents and you don't have that kind of
headroom to spare.  Your LED itself creates another.  It's not likely
to allow 1.5A with only 5V of drive, under any circumstance.  These
are guesses, admittedly.  But what this seems to say is that you
probably need another voltage rail, at a minimum, if you want to get
up to 1.5A on your LED.

If you can live with less than that but still want a lot more than
150mA, the perhaps your LED will allow ... hmm ... say (4.4V-3.3V)/2
... or about 500mA, let's call it, assuming you can limit your BJT
switch to a Vce of 0.6V or less.  And no more than (4.8V-3.3V)/2 or
about 700mA.  I think that's the best you can hope for.  But I'd plan
no more than 500mA, after some testing first.  In this case, you can
keep your rail, maybe, but you have to lose the darlington.

Jon

Thanks, Jon that's a very helpful analysis.

No problem. I'm a hobbyist, though. So be warned. I'll probably
catch some flak from someone on the above. But I'll learn from it, if
I do. So that's fine.

I'll have to scope it out in the next couple of days.

It's not hard and it can be a great help in hand-computing a few
important things that will help you in a realistic design. One thing
is to drive different currents through the LED (assuming you have a
desk power supply that lets you set current limits and monitor
voltages, as I do) and list a few interesting data points on a sheet
of paper. From there, you can develop a very simple and workable
guess about the ON voltage and the intrinsic resistance (which isn't
realistic across all possible circuit design needs, but is very simple
for planning purposes and will cover your needs here.) I'll talk
about this model more, below. Also, it will tell you a lot about what
your 2N2222s are really doing for you.

And I'll consider a higher voltage rail
(that just means soldering that 7805 on the MCU board, where I'd left
it out before... oh, yeah, and probably decoupling caps if I'm
snapping off pulses like that...)

Well, I imagined you already had a 5V rail. A higher rail would be
more than that and the 7805 probably isn't right.

If 500-700 mA gives me the brightness I want, fine.

Well, I don't think it will. I'm guessing that you are already seeing
a little more than 150mA. Tripling that will definitely help, but as
our eyes are logarithmic against that change, so I'm betting you will
imagine more like about 30-40% brighter. Not 3X. You need to really
crank hard on the LED or else use a longer period of time for your
pulse -- but I think you already mentioned that causes its own
problems in your application.

I'm betting you need a higher rail. Question will be, will the LED
last long or stay as bright with this kind of abuse? There are a lot
of failure mechanisms, but you are probably looking at delivering a
couple of milli-Joules in a very short time. Optical output degrades
with higher pulsing -- for example, HP's book on LEDs suggests that
30% loss of brightness occurs when driving at 5X the rating for 1000
hours, but where less than 3% loss occurs driving at 1X for that long.
That's direct gap LEDs. The indirect gap LEDs are worse. There is
moisture creep into the package and if that vaporizes from some pulse,
it's not so good. Plus thermal fatigue due to different expansions of
lead frame, plastic, junction coating, die, bond wires, and so on.
Then there is annealing of metals, which is strongly temperature
dependent. And at higher temps, the plastic, which normally has a
fairly stable expansion coefficient, can see it's coefficient
amplified crossing over some unknown T. Chemical degradation... well,
the list goes on. In any case, if you really do manage to whack them
with 1.5A per pulse, you may see some significant reduction in overall
lifetime. Just keep it in mind, assuming the thing doesn't just blow
up, of course!

I'm not looking to
laser etch anything. I just want LEDs that aren't pitfully dim. Your
discussion gives me hope that I can get there.

Well, time will tell.

There are other considerations in terms of what humans perceive. A
lot of it is about contrast. I don't know exactly what your setup
looks like, or how it is expected to be used, but there often are a
lot of things you can do to improve the contrast and thus improve
visibility instead of relying only on hammering your LEDs with huge
currents. You might want to investigate those aspects before planning
on using an electronic jack-hammer on your poor LEDs.

I actually don't have a current-limiting resistor on the collector
leg.

I gathered that. I didn't include them in the schematic, either.

When occasionally a software glitch leaves the LED on (I switch
it off quick), it's bright. Once it even started going a bit green,
but I shut it down just in time. (That color change is unmistakable.)
And it gets hot after just a few seconds.

I bet.

As for the LED analysis, I'm only slowly figuring out how to model
LEDs in my head; I'll go through your discussion above in detail when
I have time.

A very simplified LED model is:

V(I) = R*I + Von

You just need to supply Von and R. That's why I wrote 3.3V and 2
ohms, as one of my guesses. More realistic models will use the y-axis
cross point for the 'saturation' current (it's a theoretical offset,
usually not directly measured but instead taken using a straight line
slope from some set of measured points back to the y-axis current) and
an Rs value, a funky N factor (emission coefficient, I think I recall)
which shows up in the power of an expression using e, and a few other
values. But the above equation is often good enough for "government
work." It just says, you "need Von voltage at least to get anything
out and R*I more than that for any chosen I."

Does anyone here have a favorite resource or book about circuit design
with LEDs?

Yes. The one I keep handy is HP's old (old enough that they cover a
whole lot and don't expect you to run around finding other references,
yet not so old that it doesn't have a lot of very useful ideas that
remain useful today) "OPTOELECRONICS: FIBER-OPTICS APPLICATIONS
MANUAL," 2nd edition. Get it.

I've found a few good websites, but many of them are mostly
app notes for somebody's IC. I've had a great time with TLC5940s, but
they're overkill if all I want to do is flash.

Best of luck with all this.

Jon

 

[mj]

On May 4, 2:02 pm, Rich Grise <richgr...@example.net> wrote:

On Mon, 04 May 2009 08:54:02 -0700, mj wrote:
On May 4, 7:52 am, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:

I have exactly that here, made it for strobe tests.
White LED too, uses an 8 pin PIC, and 2 transistors to get some high current.
Want the asm source? Could perhaps still find it.

Actually, it's the circuit to pump current through those LEDs that I
need. My code works already. It works, but the light is feeble. The
asm source wouldn't do me much good, since I'm using AVR. (Now, there,
I'm going to get called scum again!)

But I would love to try out your circuit!

Doesn't anyone teach you googlies about the other side of google? I
just now put "circuit to pump current through an LED", without quotes,
into google's web search window, and got "about 227,000" hits.

Do your own homework.

Good Luck!
Rich

I tried adding extra snark to the circuit, and the LED is no
brighter. As I expected. Turns out snark sheds no light at all.

I did find some good articles on LED overdriving, but nothing at so
low a duty cycle.

It's not homework, just a personal project I get to work on a couple
of times a week.

But hey, thanks anyway.

 

[mj]

On May 4, 2:11 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

On Mon, 4 May 2009 08:49:44 -0700 (PDT), mj <eluc...@gmail.com> wrote:
snip
Actually, I'm actually doing this for a dozen LEDs at once. A rotating
transparent disk has [A-Z0-9 ] printed just inside the circumference
around the circle. A motor spins the disk at 20-50 RPM (controlled by
the MCU with PWM).
snip

Did you mean to say RPM??  At as low as 20 RPM, you'd be talking about
taking 3 seconds to make one revolution.

Jon

Whoops, no--rps.

 

On May 4, 1:49 pm, "Joel Koltner" <zapwireDASHgro...@yahoo.com> wrote:

What kind of professor puts, "Do you believe..." questions on an engineering
exam anyway? He might as well have asked you if you believe in
anthropomorphic global warming or the tooth fairy.

Anthropogenic, not anthropomorphic.

 

[Jim Yanik]

James Arthur <bogusabdsqy@verizon.net> wrote in
newsdELl.2340$fy.2193@nwrddc01.gnilink.net:

legg wrote:
On Sat, 2 May 2009 17:15:50 -0700 (PDT), Mark-T
MarkTanner50@gmail.com> wrote:

DId anyone here see the problem presented in
the Science section of NY Times last week?
Quite startling, to see something so sophisticated
in a 'general readership' publication.

Is it solvable without a calculus of variations approach?

At least it makes more 'sense' than the duck and the fox.

There's no reason for the duck to leave the pond.

The only problem I see with the elaborate solution is the assumption
that the obviously ill 'killer' rabbit will react in any way to the
presence of suits around the pond's periphery. After all, a rabbit
with any sense wouldn't be in the middle of a pond in the first place.

RL

In real life, the rabbit leaps from the pond and slaughters all
concerned with his "big, nasty teeth," despite Tim the Enchanters'
best efforts to warn them.

Tragic, really.

James Arthur

didn't Jimmy Carter get attacked by a killer rabbit in the water while he
was canoeing?

--
Jim Yanik
jyanik
at
kua.net

 

[Nobody]

On Mon, 04 May 2009 05:53:12 +0100, Eeyore wrote:

I have to agree with you.

The USA claims to be so in favour of 'free speech' yet it's the Americans
here who don't want to hear views that are contrary to their own.

Very odd.

FWIW, I'm not particularly surpised by the correlation between
believing that being a blowhard jerk is not only a constitutional
right but a patriotic duty, and not wanting to hear contrary opinions.

 

[Nobody]

On Mon, 04 May 2009 08:57:05 -0700, mj wrote:

Thanks for anyone that wants to provide some ideas.

mosfet driverhttp://ixdev.ixys.com/DataSheet/99061.pdf

14 amps, well now that ought to do it. :{)

Can someone explain to me why a MOSFET would be better here than a
bipolar?

He wasn't suggesting using a MOSFET per se, but a MOSFET *driver*.

These are designed for supplying (and sinking) short pulses of high
current, in order to charge (and discharge) the gate capacitance quickly.

 

[mj]

On May 4, 12:07 pm, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:

On a sunny day (Mon, 4 May 2009 08:28:19 -0700 (PDT)) it happened Tim Williams
tmoran...@gmail.com> wrote in
fcb2ca0a-407b-48cd-9a50-67b1890f8...@z7g2000vbh.googlegroups.com>:

On May 4, 6:52 am, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:
I have exactly that here, made it for strobe tests.
White LED too, uses an 8 pin PIC, and 2 transistors to get some high curr> >ent.
Want the asm source? Could perhaps still find it.

A PIC for blinking an LED?  Not even LED*s*, but *an* LED?

You are scum among engineers!

(Obligatory ;-) included, since *I hope* you chose a PIC for timing
reasons or something.)

Tim

Well, yes, timing reasons and low part count.
Actually I looked up the little board, only one transistor..
and the PIC 12Fsomething.. just put it away again.
Indeed I wanted to see for myself if I could get better brightness from a white LED
with short very high current pulses, then with just DC.
It is not better,
I wanted the pulses to be at about mains frequency, or at least
faster then when you would see flashes.
555 timer could do it, but I have a load of those 12Fsomething PICs, and
no 555s, so why not use the PIC?
In my view the times of analog MVBs is over, big capacitors are more expensive then chips (PICs),
and you need to keep them in stock.
Sure you can do the same with 2 or 3 transistors... But not with the same
stability.

I do not see what people have against PICs, programmable logic, you see
people here make huge complex circuits with 7400 series or even CD400 series,
or whatever, as solutions to some question.
Was it you who did a z80 setup to just display some 7 segment data while
a PIC<-- could do it faster cheaper and better?
Just a few lines of asm in a micro (I am not married to PIC either), will do away with all
but one of the chips usually.
So when you have the assembler, the programmer, the PIC, and the knowledge how to write the code,
why go out an buy something you no longer need?
Even for the simplest thing,

Geez, I thought I was the scum! I agree--for one-offs, an 8-pin DIP is
an 8-pin DIP. For production, of course, it's all about total cost.
Often dominated by board size rather than component cost.

'swhy I like I2C so much -- wiring up discrete chip select logic (not
to mention bus lines) is a PITA.

--mj

 

[David L. Jones]

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2009.05.04.18.53.06.686997@example.net...

On Mon, 04 May 2009 09:42:42 -0700, alertjean wrote:
On May 4, 8:58 am, "keith...@gmail.com" <keith...@gmail.com> wrote:
On May 4, 12:46 am, alertj...@rediffmail.com wrote:

Based on trends in mask and design costs for standard cells, vs. FGPA
capabilities, do
you believe the number of new designs per year executed in standard
cells will increase
or decrease in the future as compared with a baseline of 2007 ?

I think it will increase, what do you think ?

I think you're nuts, but you can ignore history at your peril.

Dave..You are smart..It was an exam question. But I am not convinced
by the answer professor gave me...that FPGAs will takeover standard
cell designs thereby reducing the number of standard cell designs. I
think as the performance and power of FPGAs will be bad compared to SC
designs, SC designs are always going to be winners
and I dont think FPGAs will take over.

What's the difference between an "FPGA" and a "standard cell", other than
my (more than likely inaccurate) assumption that an FPGA is simply a
collection of interconnectible standard cells?

Well, you aren't exactly wrong, but the point of FPGA's over standard cells
is that FPGA's are reconfigurable off-the-shelf devices and require no NRE.
Standard cell is basically a full ASIC with the associated NRE.

Dave.
---------------------------------------------
Check out my Electronics Engineering Video Blog & Podcast:
http://www.alternatezone.com/eevblog/

 

[David L. Jones]

--
<alertjean@rediffmail.com> wrote in message
news:98e3f191-fdd5-4ee2-900d-347854303bf4@j12g2000vbl.googlegroups.com...
On May 4, 8:58 am, "keith...@gmail.com" <keith...@gmail.com> wrote:

On May 4, 12:46 am, alertj...@rediffmail.com wrote:

Based on trends in mask and design costs for standard cells, vs. FGPA
capabilities, do
you believe the number of new designs per year executed in standard
cells will increase
or decrease in the future as compared with a baseline of 2007 ?

I think it will increase, what do you think ?

I think you're nuts, but you can ignore history at your peril.

Dave..You are smart..It was an exam question. But I am not convinced
by the answer professor gave me...that FPGAs will takeover standard
cell designs thereby reducing the number of standard cell designs. I
think as the performance and power of FPGAs will be bad compared to SC
designs, SC designs are always going to be winners
and I dont think FPGAs will take over.

It's very hard to quantify this stuff. Do you base the figures on actual
shipped chip quantity?, number of design implemented? etc.
Standard cell ASIC's require a massive NRE investment, and this effectively
puts a cap on the number of customers who can afford to design ASIC's.
If you base the argument on number of people implementing new designs, then
FPGA's will win hands down, as even Joe Blog Hobbyist can implement FPGA's.
If you look at the EDA market, then ASIC customers are getting fewer and
fewer (like down to a number you can start to count on your hands), but FPGA
tool use has been exploding in numbers for a long time. So in that respect
your professor is right.

But there will always be a big niche for custom ASIC's, the market won't
vanish.

Dave.
---------------------------------------------
Check out my Electronics Engineering Video Blog & Podcast:
http://www.alternatezone.com/eevblog/