Transformer -- rated power

g better.

4v xformer runs very cool especially compared to NOT using the driver and m= aking a direct DC connection to the led, which makes the xformer nice and w= arm.

well for full brightness.

cause it's on and off based on the duty cycle) but again -- the current is = still there.

ep up" going on creating less current demand.

If its a switched mode driver, it transforms 24v 50mA or so down to 3v

330mA

issipate? (and not really current?)

Transformers hahve VA ratings, output v times output i.

omething smaller say 250ma or so? BECAUSE --

50mA

:)

NT

better.

xformer runs very cool especially compared to NOT using the driver and making a direct DC connection to the led, which makes the xformer nice and warm.

for full brightness.

it's on and off based on the duty cycle) but again -- the current is still there.

going on creating less current demand.

dissipate? (and not really current?)

something smaller say 250ma or so? BECAUSE --

What driver circuit are you using?

John

something I got off ebay from hong kong -- it doesn't have it's own trnsformer but can run a string of series connected 1w led's (up to 6 at 350ma) depending on DC input voltage. don't know what the chip is but there are 3 or 4 ic's on it.

I'm rather confused by NT's answers -- (sorry).

There is a difference between power and current, AC and DC.

What generates heat is how much power is dissipated by a device. You can use

10M amps and generate less heat than 10mA.

I'm not clear how you have the transformer hooked up but it seems the driver itself maybe "soaking" up some of the power dissipation and you are neglecting it.

For example

Vcc--R--L--Gnd

Where L is the LED

will have a different power dissipation for R than

Vcc--R1--R2--L--Gnd

Now R2 will drop some voltage and therefore the power dissipation will be less in R1 than the first case. This is true even if the current is the same in both cases.

Your driver is most likely dissipating heat that is "missing" in the transformer.

better.

xformer runs very cool especially compared to NOT using the driver and making a direct DC connection to the led, which makes the xformer nice and warm.

for full brightness.

it's on and off based on the duty cycle) but again -- the current is still there.

up" going on creating less current demand.

dissipate? (and not really current?)

something smaller say 250ma or so? BECAUSE --

Probably one of those inexpensive little DC->constant current Chinese modules.

This is one of the SMPS chips that are used:

If it actually meets the 80%-efficient claim on the datasheet, a 3V

300mA LED will require around 52mA from a 24V supply. Maybe somewhat more if they didn't count Schottky or inductor or resistive losses in the PCB, but certainly a lot less than 300mA.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

better.

xformer runs very cool especially compared to NOT using the driver and making a direct DC connection to the led, which makes the xformer nice and warm.

well for full brightness.

(because it's on and off based on the duty cycle) but again -- the current is still there.

up" going on creating less current demand.

dissipate? (and not really current?)

something smaller say 250ma or so? BECAUSE --

Anyone tried rolling their own LED house lighting? The marketplace is currently ridiculously expensive. I have high attic space, so it's trivial to walk around and install DC supplies, for example: the kitchen where we presently burn 450W and still lack for brightness. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Havn't been tempted yet. The halide lamps seem like they are still a good alternative. Ballasts are expensive, but the lamps are reasonably priced and efficient.

Look at this one:

4850 lumens from a 9000-hour 70 watt bulb! vs. 2500 hours and 1100 lumens from a typical 75W halogen.

The $41 bulbs turn out to be 40% less expensive per lumen-hour than the $4.50 halogens, and they use maybe 25% of the energy per lumen. They do require a ballast outside of the standard fixture though.

One of the problems with LED lighting is that you're generally buying the 'ballast' with every bulb.

If I was to consider it I'd look at using RGB power LEDs with DMX512 controllers to be able to adjust the color temperature.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

better.

xformer runs very cool especially compared to NOT using the driver and making a direct DC connection to the led, which makes the xformer nice and warm.

No. 330 ma is the LED _rating_. The figure you need to use for comparison is the _actual_ current drawn using each source. Also, pulses of current at 330 mA are not the same as steady current at 330 mA.

Your driver is limiting the current to a lower value than your direct connection, most likely by pulsing the current on and off.

Your "direct" connection of 24 volts to the LED isn't right. Either there is some limiting circuit or component involved, or you are killing the LED. Your 1 watt 330 mA rated LED has a voltage rating of ~3.3 volts. 24 volts is over 7 times that voltage rating. You'd need about 63 ohms series resistance to limit the current, or some other current limiting means. That resistor would get HOT. If you used a linear regulator to limit the current, the regulator would get HOT. In either case - resistor or regulator - the extra heat generated amounts to almost

7 watts. The transformer provides more energy than the LED needs. At 330 mA and 24 volts, it is providing 7.92 watts, and the LED takes only 1 watt. The resistor or linear regulator work by throwing away the excess power as waste heat.

Your driver, on the other hand, is probably a switching power supply. It works by taking only the amount of power needed from the transformer - sort of like little sips instead of great big gulps. :-) It doesn't have to throw excess power away, because it didn't take it from the transformer in the first place

Ed

it's on and off based on the duty cycle) but again -- the current is still there.

up" going on creating less current demand.

dissipate? (and not really current?)

something smaller say 250ma or so? BECAUSE --

John --

it's this one

there is some feedback here in replies but isn't clearing up my confusion.

based on the dc input voltage you can drive 1 to 6 led's in series at 330ma -- whether you run one led or six led's there is always 330ma in the series circuit, using my VOM.

SO -- back to the questions I had in my original post -- really appreciate the help. the transformer question in particular.

Which is why I am tempted to roll my own. Wonder how many Lumens you can get from a white LED? I'm amused by making a "star" studded ceiling ;-) And a switcher to run a bunch in series would be trivial... even a mechanism to bypass a fried LED would be easy.

...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

I'll repeat the specific question again --

the 330ma is there and very real because that is what my VOM is reading, so WHY does my 500ma transformer feel so cool with the switching driver?

because the transformer is really rated for use with a continuous (always on) power supply?

so, feasibly, I could use something that is rated for less current? even less than the 330ma required?

am I making sense?

WHY does my 500ma transformer feel so cool with the switching driver?

power supply?

than the 330ma required?

The transformer feels cool because it is at a lower temperature.

--
We have failed to address the fundamental truth that endless growth is 
impossible in a finite world.

WHY does my 500ma transformer feel so cool with the switching driver?

power supply?

than the 330ma required?

Perhaps this is more useful:

The controller you are using is a switch-mode device. Its regulates it's output current to the 330ma you are reading but if you read the input current to the regulator it will be much less. Forgive the horrendous simplification but essentially the regulator is a power converter and is controlling the current output by increasing the output voltage to whatever is needed in this case about 3 volts which is roughly equal to

1 watt. To do this the regulator needs only a bit more than 1 watt of power input (it is not 100% efficient) so it needs only about 50 ma from the transformer 24v x 50ma = 1.2 watts.

--
We have failed to address the fundamental truth that endless growth is 
impossible in a finite world.

circuit, using my VOM.

help. the transformer question in particular.

OK, that's a switching power supply.

As an analogy, imagine the difference between a clutch and a gear set. Both can deliver torque from a fast-rotating shaft into a slow-turning load, but the gear is much more efficient. The clutch gets hot, the gears don't.

A buck switching regulator applies the 24 volts to the LED string at a low duty cycle, 20% maybe, through an inductor. The 24v power source supplies 300 mA, but only 20% of the time, so the actual average current the supply has to deliver is only 60 mA or so. The switching regulator "gears it down", which a simple series resistor wouldn't.

Gory details:

John

circuit, using my VOM.

help. the transformer question in particular.

App note for chip:-

I'd like to see more parts in that TO252-5 package.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

"mkr5000"

** Iron cored AC supply transformers are rated purely on long term temperature rise under continuous load.

For short term and intermittent loads, secondary currents up to 5 times the nominal rating are available.

At higher loads, the output voltage will be less according to the " regulation factor". If the regulation factor is say 10% at rated load, then it will be 50% at 5 times that load - so only half voltage is available.

... Phil

There was some discusion a while back about LED failure modes, but I forget the results. If theey tend to fail short then there's no problem, otherwise one could bypass each LED with a zener... Hmm, that works for either failure mode as long as the current source has enough compliance.

Grant.

circuit, using my VOM.

help. the transformer question in particular.

That's already answered. More LEDs in series increases the voltage, therefore increases V * I, therefore power. Easy!

It's the switchmode regulator converting LED current at low voltage to low current at 24V, same power, minus the switchmode's conversion effficiency.

Which part of that you having trouble with?

Grant.

Why is it I doubt that statement? 10MA might be seen in an aluminium pot line, I can't think where else, arc smelter?

:o)

Grant.