Author Topic: "driverless" led lamp  (Read 5611 times)
Alights
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"driverless" led lamp « on: January 22, 2013, 10:05:22 PM » Author: Alights
http://www.1000bulbs.com/product/88852/LED-LCA12C18027K1.html?utm_source=facebook&utm_medium=social&utm_campaign=archipelago_led

Never heard of a driverless led lamp! In a nutshell its a more reliable one eliminating driver failure which is the weak point of led technology
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Medved
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Re: "driverless" led lamp « Reply #1 on: January 23, 2013, 12:43:39 AM » Author: Medved
That ad is definitely a bunch of lies:
- The high voltage AC chips are nothing new, they are on the market already many years, the first I've seen was the ACRiche family from SSC. They are illuminating my kitchen from the ceiling for about fift'h year. Bought at Farnell/Element14, but they were quite expensive at that time... In the meantime even other companies started to offer such chips too.

- They are not totally driver-less, although they suffice with simple series resistor (the simplest form) and/or PTC (compensate some mains variation). This make the assembly less efficient, but not as big price to pay for the reliability. Moreover the small DCDC converters are not 100% efficient anyway, so the difference is not as large.

- The biggest lie (technically important) is the statement "No driver also means the bulb is smaller than other LED light bulbs since a large aluminum heatsink is not needed". In the "other LED" the heatsink is there to take away the heat generated by the LED's and keep them cool. As these LED's are less efficient, they need in fact larger heatsink for the same light output in order to keep the temperature the same.

Internally they are made as about 40..160 (depend on version) LED junctions on one common chip connected in antiparallel pairs (so one light for one polarity, the second for the other polarity) and these pairs are then interconnected into a series string. And then multiple such chips are eventually packaged together and bonded either in series or parallel, to match the target mains voltage. The higher chip complexity make them more expensive, but as well the extra on chip interconnect metalization block some light and cost an extra chip area, so only about 60% of the die actually emit light, the rest are isolation structures (oxide trenches).
Some versions use resistive on-chip metalization, so do not need the external resistor, but then the resistor's power dissipation is to be handled by the LED component itself, making the thermal design of way more challenge.
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dor123
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Re: "driverless" led lamp « Reply #2 on: January 23, 2013, 02:43:49 AM » Author: dor123
If the LED inside the LED lamp in this AD, is a regular 5mm through holes LED, than the heatsinking will be useless, as there are no ways for these LEDs to release their heat to the outside. So even the best heatsinking willn't help in that case.
Heatsinking can only work for SMD LED and HPLEDs, as these are surface mounted directly to the heatsinking, and so they can depress their heat more efficienctly by this way.
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Medved
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Re: "driverless" led lamp « Reply #3 on: January 23, 2013, 04:12:02 AM » Author: Medved
@dor:
Clearly it is not, the 50 of 5mm LED's won't fit there...
The ACRiche I was talking about is sold in the form of a bit larger format of power capsules (the chip is bigger and there are multiple of them inside to reach the 2W LED; the 1W would be on the resistor).
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dor123
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Re: "driverless" led lamp « Reply #4 on: January 23, 2013, 04:28:16 AM » Author: dor123
Medved: I meaned that this lamp have just a single 5mm LED, based on its appearance.
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I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

I only working with the international date format (dd.mm.yyyy).

I lives in Israel, which is a 220-240V, 50hz country.

Medved
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Re: "driverless" led lamp « Reply #5 on: January 23, 2013, 04:53:26 AM » Author: Medved
Medved: I meaned that this lamp have just a single 5mm LED, based on its appearance.

With 3W, that would blow in an instant...
Believe me, it is not as bad, even the most cheapest design have to really work at least few hours in the showroom...

Technically that is not bad concept, the heatsink is not as ridiculously small for 2W LED. Given there are involved way lower currents than it is usual for LED's, the die bonding (the most troublesome part of any semiconductor when it come to high temperatures) could withstand way higher temperatures. And what helps as well is the AC current, as the most problematic are the bondwires carrying current from the chip, as the electromigration tend to deplete the bondpad around the wirebond ball (the aluminum tend to dissolve into the gold bondwire).
Moreover as the chip is large for the given power, it have way lower thermal resistance towards the heatsink, so even when the heatsink run hotter, the chip may still be on the same temperature as "standard" high power LED's.
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Re: "driverless" led lamp « Reply #6 on: March 04, 2013, 03:42:23 PM » Author: arcblue
I have one of these lamps, except it is an A-19 globe and medium base. Otherwise, the design looks identical.

It is a surface-mount LED chip with a very orange-looking phosphor. The lamp's colour is nice. It dims on a standard dimmer switch, but not nearly as low as an incandescent.  The heat is dissipated into the lamp's cap, which seems to act as a heat sink. Thus, the socket gets very hot, and the bulb's glass does not. I'd suggest the lamp should be used with ceramic sockets and burned base up.

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Luminaire
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Re: "driverless" led lamp « Reply #7 on: March 24, 2013, 06:02:55 PM » Author: Luminaire
I'd guess it uses LEDs in pairs back-to-back so one side lights on one-half a cycle and the other on the other half and simply driven off a resistor. 

The EcoSmart fixture that uses a panel with LEDs connects directly to 120v and does not appear to have an obvious driver though... see SKU 697388 on Homedepot.com
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Re: "driverless" led lamp « Reply #8 on: March 25, 2013, 12:35:55 AM » Author: Medved
I'd guess it uses LEDs in pairs back-to-back so one side lights on one-half a cycle and the other on the other half and simply driven off a resistor. 

The EcoSmart fixture that uses a panel with LEDs connects directly to 120v and does not appear to have an obvious driver though... see SKU 697388 on Homedepot.com

Beside the back-to-back (that is sometimes called "antiparallel") configuration it have to use many of these in long chains, otherwise for the given power you would need too high current and so dissipate way too much on the series resistance.

The ACRiche's have all that fabricated on the single die (like IC's integrate many active components with complex interconnections, here are formed many isolated junctions and connected in series/parallel, all on the single chip).
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