Hey idiot ... you don't seem to even know how to read. If your mother didnt send you to school then you might try sueing the long dead lady but I'd advice you to Go back to nursery school ... I said I don't talk to idiots... so you're talking to yourself.
"Go easy on your drugs"
theJackal
-- didnt? sueing? advice you? Seems like you could use a little help with the language yourself. And as for the logic, you call me an idiot and in the same breath you say you don\'t talk to idiots. And keep posting. And posting. And posting. You just can\'t keep from beating yourself up, can you, ya fuckin\' loser?
current and
-- You\'re wrong and, as usual, you don\'t even know why.
The only way the lamps can give the same light output is if they have the same current and voltage across them assuming they are of the same type.
His idea of connecting them in parallel is wrong. Check my earlier post on the matter.
"Go easy on the whisky"
theJackal
current and
Two "lamps" with the same part number and same current will have slightly different voltages because they're different. Close is good, but it's not exact.
Two lamps with the same part number and same current selected to have the "best match" voltage from a bin of parts will still have different light output levels due to differences in phosphor coating (for white LEDs) thermal conductivity of the package (or system) and other physical characteristics of the LED materials, packaging, and environment.
The normalized luminance versus current curves for the individual devices is similar in shape across production suggesting that a first-order match of the LEDs by setting the current of each LED for a fixed luminance will result in a "good" match (though not exact) as the current is increased or decreased from the calibration point. The differences of luminance at other proportional current levels and at other thermal operating points are second-order mismatches.
By feeding each LED with a controllable current, the voltage will be defined by the LED. These constant-current LEDs can be in series or parallel requiring series or shunt regulation, respectively; it's just easier to have series regulators in a parallel configuration. It also makes the proportional control much simpler.
same current and
-- No, thats _not_ what you said. What you said was that two lamps with identical currents through them and identical voltages across thenm will have the same light output, and that\'s not right.
-- Ya like to dish it out, but ya can\'t take it, huh? Goddam pussy.
parallel
branch , but
decrease in
You'd then have
take into
of the LED.
--
You know what? You\'re about the stupidest sonofabitch I ever ran
across.
Here:
Ya take seven LEDs and hook them up in series with seven pots, like
this, and hook them all up in parallel with a _voltage_ source
(_not_ a current source) like this:
+V>----+--------+--------+--------+--------+--------+--------+
| | | | | | |
[POT]
-- Sharp, as usual! Very nice, thanks. :-)
same current and
Note thats why I said above ... if they have the SAME current and voltage .
In my first post in the thread I mentioned that. I would include dopant density variations which affect the resistivities of semiconductors.
Here you correctly say you set the currents of each LED for a fixed illuminance the below you contradict yourself by saying a parallel or a series connection of LEDs is fine. A parallel connection sets the Voltage of each LED as fixed and NOT the current.
The radiant power is a function of Photon emission. Photon emission is determined by hole electron recombination currents in the quasi neutral n and p regions of the Light emitting diodes.
A series regulator in a parallel connection IS totally bad. Because you are changing not only the voltage and current of 1 LED but of ALL the other LEDs . That doesn't happen if its in a series connection.
"Go easy on the whisky"
theJackal
If you think about it, he's got to be lying. Otherwise, how did his post get out? ;-)
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
He doesn't know the difference between "delete" and "filter"?
Cheers! Rich
-- Yes, that\'s why toward the end of the article I wrote: "So, under those conditions it looks like what\'s needed is about a 15 ohm 15 watt adjustable power resistor." What I was thinking was along the lines of an adjustable vitreous enamelled wirewound reesistor like a an Ohmite Type 210 or a Huntington AVT, with a Huntington 25 ohm 50 watt unit available from Digi-Key for $4.50 qty 1. >If the passive >approach were used, a combination of fixed resistors for a set point along >with more reasonable potentiometers might be warranted. I agree, but I think that using a single adjustable fairly high-power resistor instead of a rheostat and an assortment of fixed resistors per LED would be even cheaper. Hard to beat $4.50 per LED, no?
illuminance
of LEDs is
current.
determined by hole
Light
changing not
doesn't happen if
I am suggesting 7 regulators for 7 LEDs. Of *course* connecting 7 LEDs in parallel directly with one series regulator will not provide a solution. Of *course* connecting 7 LEDs in series with one shunt regulator will not work. If one "LED stage" is defines as an LED and a regulator, 7 "LED stages" can be connected in parallel if the "LED stage is built with a series regulator and 7 "LED stages" can be connected in series if the "LED stage is built with a shunt regulator.
I don't contradict a thing. EACH LED is fed with a controllable current. Separately. Not "all LEDs are fed with A controllable current."
-- My intent when posting the article wasn\'t to describe an efficient system, it was to give the Jackal something to chew on. I, personally, have no particular interest in high-powered LEDs, but if you do, go for it! And good luck!
-- Why?
If I get you right ... you are connecting a series resistor/regulator in each parallel branch of the LED array. Suppose you want to brighten a LED you'd decrease the resistance in that branch , but that would increase the current flowing through it , which would then cause a decrease in the currents flowing to the other LEDs ... so those would become dimmer . You'd then have to work on the resistors in the other LED branches. Besides you'd have to take into account the limiting current and the non linear voltage current characteristic of the LED.
theJackal
Any posts containing "John Fields" are automatically deleted by my system
YES! You've got it now. The only major concept that you aren't seeing is that a constant-current series regulator that uses feedback from the current running through the LED *won't* be affected by the other LEDs current changes as long as the supply is properly regulated. Constant-current loads need a supply with a voltage that can meet the LED voltage drop plus regulator "dropout voltage" for all the LEDs, supplying enough current to accommodate all 7 LEDs at full current.
If you stop thinking "resistors" and start thinking "regulators" everything can come together.
The need to ramp the intensity up and down with a single control - one dimmer for 7 matched intensities - means that the regulators must track each other as the brightness is increased and decreased. If the 7 regulators run from 75% to 100% rated current to match brightnesses for a particular batch of LEDs, half-power would servo those regulators to 37.5% to 50% of rated current proportionally.
These high-current LEDs need a transistor (I'll use n-channel MOSFETS), current sense (small value resistor for my implementation), an amplifier with feedback to maintain a fixed current through the sense resistor through the gate drive voltage, and a method to calibrate the individual LEDs and present a "master" brightness. I may use potentiometers with tap to the opamp and rails of ground and "master brigtness voltage" or use an 8-channel multiplying DAC: change the reference voltage and the outputs scale.
The main supply just needs to supply a voltage that will have all the regulators properly regulating (or all the op-amps out of saturation).
--- After reading your post again, I think you're talking pie in the sky. Sure, you can lower the power supply voltage to get an operating window with less loss, but you still have to waste the energy to make the bright LEDs as dim as the dull ones to start out with if you use the same gross power supply for them all, and since you're not talking PWM or some reactive scheme you're talking DC, so you're stuck. It's still inelegant brute force, but you're just using a smaller sledgehammer.
Then you've still got the problem of making the lamps' luminance track as they're being dimmed, so you need an array of scalable voltage controlled current sources which will vary the current into the lamps depending on some nebulous open-loop calibration done at what? one point?
If you want to go with that, then you've got to admit that all your scheme does is trim the waste, not get rid of it.
-- John Fields Professional Circuit Designer
If the currents are supplied from a fixed voltage through resistors, when you change the power supply voltage the brigtnesses will not track unless you can guarantee an exact match of the LED voltages. I wouln't trust the match to be sufficient for small voltage drops in the resistors. If one chooses to use a large voltage drop across the resistors (low efficiency) then the match is very good until the brightness is reduced significantly and the LED voltages again become significant.
It may not be cost-effective to use potentiometers rated at the necessary power levels to accommodate the large voltage drops. If the passive approach were used, a combination of fixed resistors for a set point along with more reasonable potentiometers might be warranted.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.