LED wiring Series or Parallel 110 or 12v (for Power Efficien

[ehsjr]

John Fields wrote:

On Sun, 08 Jan 2012 00:43:27 -0500, ehsjr <ehsjr@nospamverizon.net
wrote:


So, if "bulletproof" at higher cost trumps efficiency at lower
cost, choose the LM317 approach. If efficiency at lower cost
trumps "bulletproof", choose the single resistor. And if both
"bulletproof" and low cost have to be part of the design,
sacrifice efficiency and brightness and use higher value
resistors. The OP's primary requirement was efficiency. Next
was low cost - implied or stated, I don't remember which.
Then there was a question about whether connecting directly
to the mains was a safe approach. Mixing all that together
yielded the posted design. Do you have a design that does
all of that?

Ed


---
Just for fun, I went back to your constant current circuit to see what
would be required to drive the OP's 48 LED, 30mA string from the mains
and built this, in the real world.


+-----+ R1 U1 R2
120AC>---|~ +|---[100R]-+-[LM317]---[39R]-+
| | | | |
| | | +------------+
| | [3.9ľF] |R3
| | |C1 [LED STRING]
| | | |4400R
120AC>---|~ -|----------+-----------------+
+-----+

It works pretty well,

LINE ACIN I(R3)
VRMS mADC
-----+------+-------
LOW 108 28.24
NOM 120 30.37
HIGH 132 31.9

is dirt cheap and survives line surges, but I haven't done any spike
testing yet.

Maybe tomorrow.

Anyway, I just thought I'd run it up the flagpole and see if anyone
salutes.

Nice. R1 needs to be higher - say 470 - to accommodate 132V ACIN,
and that reduces the deltaV across the 317 for all line voltages.
Also, I'm a wimp where it comes to running LEDs near their ratings,
so I'd use 51 ohms or more for R2 to keep the current lower than
30 mA.

Ed

 

[John Fields]

On Tue, 10 Jan 2012 22:40:13 -0500, ehsjr <ehsjr@nospamverizon.net>
wrote:

John Fields wrote:
On Sun, 08 Jan 2012 00:43:27 -0500, ehsjr <ehsjr@nospamverizon.net
wrote:


So, if "bulletproof" at higher cost trumps efficiency at lower
cost, choose the LM317 approach. If efficiency at lower cost
trumps "bulletproof", choose the single resistor. And if both
"bulletproof" and low cost have to be part of the design,
sacrifice efficiency and brightness and use higher value
resistors. The OP's primary requirement was efficiency. Next
was low cost - implied or stated, I don't remember which.
Then there was a question about whether connecting directly
to the mains was a safe approach. Mixing all that together
yielded the posted design. Do you have a design that does
all of that?

Ed


---
Just for fun, I went back to your constant current circuit to see what
would be required to drive the OP's 48 LED, 30mA string from the mains
and built this, in the real world.


+-----+ R1 U1 R2
120AC>---|~ +|---[100R]-+-[LM317]---[39R]-+
| | | | |
| | | +------------+
| | [3.9ľF] |R3
| | |C1 [LED STRING]
| | | |4400R
120AC>---|~ -|----------+-----------------+
+-----+

It works pretty well,

LINE ACIN I(R3)
VRMS mADC
-----+------+-------
LOW 108 28.24
NOM 120 30.37
HIGH 132 31.9

is dirt cheap and survives line surges, but I haven't done any spike
testing yet.

Maybe tomorrow.

Anyway, I just thought I'd run it up the flagpole and see if anyone
salutes.


Nice. R1 needs to be higher - say 470 - to accommodate 132V ACIN,
and that reduces the deltaV across the 317 for all line voltages.

---
If I used 500 ohms it'd drop 15V at 30mA - which wouldn't let me get
30mA into the LED string with low line in - and it'd dissipate 450
milliwatts when there was 30mA through it.

The trick to why it works with 100 ohms in there is that the LM317
doesn't start waking up until the voltage differential between the
input and output is a volt or so, so until then it acts pretty much
like a saturated NPN series pass transistor and the voltage across the
load will follow the input voltage minus a volt or so.

Then, as the voltage across the load rises, the current through it
will increase until the voltage dropped across R2 increases to 1.25
volts, when the LM317 will start limiting the current into the load to
30mA until the voltage across R2 falls to less than 1.25 volts later
on in that mains half-cycle.

Doing it that way only drops 3 volts across R1 and causes it to
dissipate 90mW with 30mA through it.

Also, the value of C1 was chosen to allow it to charge only to the
voltage required to get 30 mA into the string at low line, with the
LM317 doing the required limiting to keep the current in the string
relatively constant from low line to high line.

I've posted some photos to abse:

news:ng0ug7hf2jrhh49sn1gppa0betc05juu55@4ax.com

I didn't post any of the output voltages into the LED string, and I
want to get this on its way, so I'll do it later on this afternoon
when I have more time.

Also, I'm a wimp where it comes to running LEDs near their ratings,
so I'd use 51 ohms or more for R2 to keep the current lower than
30 mA.

---
Tsk, tsk, tsk.

--
JF

 

[ehsjr]

John Fields wrote:

On Tue, 10 Jan 2012 22:40:13 -0500, ehsjr <ehsjr@nospamverizon.net
wrote:


John Fields wrote:

On Sun, 08 Jan 2012 00:43:27 -0500, ehsjr <ehsjr@nospamverizon.net
wrote:



So, if "bulletproof" at higher cost trumps efficiency at lower
cost, choose the LM317 approach. If efficiency at lower cost
trumps "bulletproof", choose the single resistor. And if both
"bulletproof" and low cost have to be part of the design,
sacrifice efficiency and brightness and use higher value
resistors. The OP's primary requirement was efficiency. Next
was low cost - implied or stated, I don't remember which.
Then there was a question about whether connecting directly
to the mains was a safe approach. Mixing all that together
yielded the posted design. Do you have a design that does
all of that?

Ed


---
Just for fun, I went back to your constant current circuit to see what
would be required to drive the OP's 48 LED, 30mA string from the mains
and built this, in the real world.


+-----+ R1 U1 R2
120AC>---|~ +|---[100R]-+-[LM317]---[39R]-+
| | | | |
| | | +------------+
| | [3.9ľF] |R3
| | |C1 [LED STRING]
| | | |4400R
120AC>---|~ -|----------+-----------------+
+-----+

It works pretty well,

LINE ACIN I(R3)
VRMS mADC
-----+------+-------
LOW 108 28.24
NOM 120 30.37
HIGH 132 31.9

is dirt cheap and survives line surges, but I haven't done any spike
testing yet.

Maybe tomorrow.

Anyway, I just thought I'd run it up the flagpole and see if anyone
salutes.


Nice. R1 needs to be higher - say 470 - to accommodate 132V ACIN,
and that reduces the deltaV across the 317 for all line voltages.


---
If I used 500 ohms it'd drop 15V at 30mA - which wouldn't let me get
30mA into the LED string with low line in - and it'd dissipate 450
milliwatts when there was 30mA through it.

The trick to why it works with 100 ohms in there is that the LM317
doesn't start waking up until the voltage differential between the
input and output is a volt or so, so until then it acts pretty much
like a saturated NPN series pass transistor and the voltage across the
load will follow the input voltage minus a volt or so.

Then, as the voltage across the load rises, the current through it
will increase until the voltage dropped across R2 increases to 1.25
volts, when the LM317 will start limiting the current into the load to
30mA until the voltage across R2 falls to less than 1.25 volts later
on in that mains half-cycle.

Doing it that way only drops 3 volts across R1 and causes it to
dissipate 90mW with 30mA through it.

Also, the value of C1 was chosen to allow it to charge only to the
voltage required to get 30 mA into the string at low line, with the
LM317 doing the required limiting to keep the current in the string
relatively constant from low line to high line.

Thanks!

I've posted some photos to abse:

news:ng0ug7hf2jrhh49sn1gppa0betc05juu55@4ax.com

You're correct, and it's much appreciated. I have no idea where
I erred on the higher value for R1, except that I may have typoed
the calculator. Typo or not, it's a glaring error. :-(

I know your post made it to ABSE, because I see the post where
JT asked about it, and your response to him. The bad thing is
that your post didn't show up on news.eternal-september.org
Makes me think I'd better get a different newsgroups provider.

I didn't post any of the output voltages into the LED string, and I
want to get this on its way, so I'll do it later on this afternoon
when I have more time.



Also, I'm a wimp where it comes to running LEDs near their ratings,
so I'd use 51 ohms or more for R2 to keep the current lower than
30 mA.


---
Tsk, tsk, tsk.

Hey, that's my story and I'm sticking to it.

Ed

 

[ehsjr]

John Fields wrote:

On Tue, 10 Jan 2012 22:40:13 -0500, ehsjr <ehsjr@nospamverizon.net
wrote:


John Fields wrote:

On Sun, 08 Jan 2012 00:43:27 -0500, ehsjr <ehsjr@nospamverizon.net
wrote:



So, if "bulletproof" at higher cost trumps efficiency at lower
cost, choose the LM317 approach. If efficiency at lower cost
trumps "bulletproof", choose the single resistor. And if both
"bulletproof" and low cost have to be part of the design,
sacrifice efficiency and brightness and use higher value
resistors. The OP's primary requirement was efficiency. Next
was low cost - implied or stated, I don't remember which.
Then there was a question about whether connecting directly
to the mains was a safe approach. Mixing all that together
yielded the posted design. Do you have a design that does
all of that?

Ed


---
Just for fun, I went back to your constant current circuit to see what
would be required to drive the OP's 48 LED, 30mA string from the mains
and built this, in the real world.


+-----+ R1 U1 R2
120AC>---|~ +|---[100R]-+-[LM317]---[39R]-+
| | | | |
| | | +------------+
| | [3.9ľF] |R3
| | |C1 [LED STRING]
| | | |4400R
120AC>---|~ -|----------+-----------------+
+-----+

It works pretty well,

LINE ACIN I(R3)
VRMS mADC
-----+------+-------
LOW 108 28.24
NOM 120 30.37
HIGH 132 31.9

is dirt cheap and survives line surges, but I haven't done any spike
testing yet.

Maybe tomorrow.

Anyway, I just thought I'd run it up the flagpole and see if anyone
salutes.


Nice. R1 needs to be higher - say 470 - to accommodate 132V ACIN,
and that reduces the deltaV across the 317 for all line voltages.


---
If I used 500 ohms it'd drop 15V at 30mA - which wouldn't let me get
30mA into the LED string with low line in - and it'd dissipate 450
milliwatts when there was 30mA through it.

The trick to why it works with 100 ohms in there is that the LM317
doesn't start waking up until the voltage differential between the
input and output is a volt or so, so until then it acts pretty much
like a saturated NPN series pass transistor and the voltage across the
load will follow the input voltage minus a volt or so.

Then, as the voltage across the load rises, the current through it
will increase until the voltage dropped across R2 increases to 1.25
volts, when the LM317 will start limiting the current into the load to
30mA until the voltage across R2 falls to less than 1.25 volts later
on in that mains half-cycle.

Doing it that way only drops 3 volts across R1 and causes it to
dissipate 90mW with 30mA through it.

Also, the value of C1 was chosen to allow it to charge only to the
voltage required to get 30 mA into the string at low line, with the
LM317 doing the required limiting to keep the current in the string
relatively constant from low line to high line.

In my prior reply I said: "I have no idea where
I erred on the higher value for R1, except that I may have typoed
the calculator. Typo or not, it's a glaring error."

Now I realize what I did - and I was correct, 100 ohms for
R1 is too low using the LM317 and figuring worst case Vin
high, but I didn't think of the high voltage version of the
LM317. Your circuit using the high voltage version is better.

The wasted power will always be the dissipation of R1 plus the
dissipation of the LM317, so it really doesn't matter how much
is wasted in R1 in terms of circuit efficiency.

Ed

I've posted some photos to abse:

news:ng0ug7hf2jrhh49sn1gppa0betc05juu55@4ax.com

I didn't post any of the output voltages into the LED string, and I
want to get this on its way, so I'll do it later on this afternoon
when I have more time.



Also, I'm a wimp where it comes to running LEDs near their ratings,
so I'd use 51 ohms or more for R2 to keep the current lower than
30 mA.


---
Tsk, tsk, tsk.

 

[John Fields]

On Fri, 13 Jan 2012 14:04:35 -0500, ehsjr <ehsjr@nospamverizon.net>
wrote:>>

In my prior reply I said: "I have no idea where
I erred on the higher value for R1, except that I may have typoed
the calculator. Typo or not, it's a glaring error."

Now I realize what I did - and I was correct, 100 ohms for
R1 is too low using the LM317 and figuring worst case Vin
high, but I didn't think of the high voltage version of the
LM317. Your circuit using the high voltage version is better.

The wasted power will always be the dissipation of R1 plus the
dissipation of the LM317, so it really doesn't matter how much
is wasted in R1 in terms of circuit efficiency.

Ed

---
True, but with the mains varying +/- 10% about the 120V nominal, R1's
being equal to 470 ohms won't allow the current - over the range of
mains variations - into the LED string to be the 30mA the OP asked
for.

With R1 equal to 100 ohms, and a 4400 ohm load resistance, (the
equivalent resistance of the LED string) the voltage across the LM317
never exceeds the absolute maximum rating at high line and, with no
heat sink, the temp of the LM327's tab never exceeds about 65C with a
25C ambient, so the circuit's pretty safe with a standard LM317.

Transient protection is something else, again, and the HV may have an
advantage there due to its inherent standoff.

Any thoughts?

--
JF

 

[ehsjr]

John Fields wrote:

On Fri, 13 Jan 2012 14:04:35 -0500, ehsjr <ehsjr@nospamverizon.net
wrote:


In my prior reply I said: "I have no idea where
I erred on the higher value for R1, except that I may have typoed
the calculator. Typo or not, it's a glaring error."

Now I realize what I did - and I was correct, 100 ohms for
R1 is too low using the LM317 and figuring worst case Vin
high, but I didn't think of the high voltage version of the
LM317. Your circuit using the high voltage version is better.

The wasted power will always be the dissipation of R1 plus the
dissipation of the LM317, so it really doesn't matter how much
is wasted in R1 in terms of circuit efficiency.

Ed


---
True, but with the mains varying +/- 10% about the 120V nominal, R1's
being equal to 470 ohms won't allow the current - over the range of
mains variations - into the LED string to be the 30mA the OP asked
for.

Yup. That's why your 100 ohms is better than the 470 (which is
too small, anyway, with the regular LM317) if using the HV
version LM317.

With R1 equal to 100 ohms, and a 4400 ohm load resistance, (the
equivalent resistance of the LED string) the voltage across the LM317
never exceeds the absolute maximum rating at high line and, with no
heat sink, the temp of the LM327's tab never exceeds about 65C with a
25C ambient, so the circuit's pretty safe with a standard LM317.

Here's where I'm missing something: with AC in at 132, the peak
after the bridge is around 185. With 3V across R1, that's 182
on the input side of the LM317, and 132 on the output side,
exceeding the 37 V max Vin-Vout. Even the 470 is too small,
dropping only ~14.1 at 30 mA and yielding Vin-Vout ~39.

Transient protection is something else, again, and the HV may have an
advantage there due to its inherent standoff.

Any thoughts?

Yes, but a different topology at a lot higher cost. I'd
use a low voltage LED supply & several LED strings. The
supply takes care of the transients and safety issues, and
current limiting can be the 317 circuit or a resistor.

If using the mains-bridge-limiter design, a TVS across the
'lytic seems a good way to go, and a .1 uF should be there too.

Paul proposed a zener across the 317 and a cap across the
LEDs which should help, and you can work on the AC in
side prior to the bridge. I'd also worry about a switch
placed between the cap and the 317.

Ed