LED lamp failure analysis – GU10 230VAC 7W

This article is about an inexpensive GU10 230V 7W LED lamp.

Like so much inexpensive Chinese lamp product, it has not markings on the exterior or the lamp (eg voltage, current, power), but the product was sold as 7W and the box had that printed on it.

The lamp failed after less than 100h service, switching on and off intermittently symptomatic of a heat related problem.

Above is the dismantled lamp. Interestingly the LED driver PCB has “Q-3-5*1W” etched into the board, so presumably it is actually a driver for 5 series 1W white LEDs. So much for the claimed 7W, LED product performance claims are often a fraud, more so when the Chinese are involved. Continue reading LED lamp failure analysis – GU10 230VAC 7W

Chinese LED ratings – LED plate drivers

I have recently purchased or attempted purchase of several nominally 18W LED circular plates and associated 230VAC drivers.

The circular LED plates all had 36 x 5730 nominally half watt white LEDs arranged as 18 parallel pairs in series.

It is difficult to find datasheets from reputable manufacturers of 5730 LED. Cree makes 5630 which are similar size (though different footprint) and also rated at nominally 0.5W.

Above is the V/I characteristic from Cree’s J series datasheet with an approximation of the 0.5W line superimposed in red. The V/I combination for 0.5W is at the intersection of the two lines, about 162mA and 3.08V. Continue reading Chinese LED ratings – LED plate drivers

Chinese T8 LED 4′ tube teardown

This article describes the internals and basic test of a no-name Chinese 4′ T8 LED replacement.

The lamp is a Type B DEP (double ended power) configuration, cool white, it requires rewiring of a traditional magnetic ballast fitting or e-ballast fitting. Don’t attempt this unless you have the needed competencies.

It has no rating label, no information about its configuration on the lamp, no warnings about compatibility… so very Chinese.

The lamp is rated at 18W 1750lm, claimed life is 50,000h but you should take that with a grain of salt. The lamps cost $6.40 ea in a pack of 10, including delivery. They were well packed and the pins had a small plastic protector.

Above, the powered end of the LED strip and the LED driver partially withdrawn from the hollow aluminium extrusion. Continue reading Chinese T8 LED 4′ tube teardown

Osram Substitube tear down

I recently purchased two packs of 2x Osram Substitube LED replacements for a T8 36W florescent tube. The price per tube was about double that of a T8 fluorescent, and claimed life was 30,000 hours.

Note that LED life is usually an estimate of the time for 50% failure. Curiously, Osram individual LEDs have lower lifetime estimates for single LEDs, strings of LEDs will have lower lifetime, and lifetime for say 5% failures would be even lower. On the basis of experience with LED lighting, it might be optimistic to think that most of these lamps will last at least 5,000h.

In the event, three of four tubes had broken glass (yes, they use a glass tube much like the T8 fluorescent tube… though not sealed at the ends), and the other was DOA, no light output.

The LED driver is attached to pins at one end of the lamp, and covered by a label over the glass. Note that there are several incompatible schemes used in T8 fluorescent replacement LEDs, the other scheme bonds the adjacent pins at each end of the lamp and connects line and neutral to opposite ends. Osram calls this a “Type A” connection, and as the name suggests if can be fitted to an ordinary magnetic ballast luminaire PROVIDED the original starter is replaced with Osram’s “LED starter” which is actually a HRC fuse of around 1A rating.

Above is the top view of the electronics. Continue reading Osram Substitube tear down

Conversion of oyster luminaire to LED

I purchased a kit to convert a oyster luminaire to single colour LED on eBay. The kit was nominally 18W, supplied with the 5730 LED plate and driver module for about $10 incl shipping.

A cautionary note: do not play with these things unless you have the necessary competencies.

The thing was packed in nothing more than a plastic mailing bag and was bent in several places in transit from China. It was not usable in that state and some LEDs were not working so my money was refunded in full (after the usual tug-o-war eventually resolved with eBay intervention). It had to be straightened to be usable, but at the risk of damaging LEDs and possibly cracking or compromising the insulation layer.

Above, after flattening the back plate, nearly half the LEDs are not working. Continue reading Conversion of oyster luminaire to LED

Milton Moore’s power supply test

When I was a student at TAFE in 1970, a teacher, Milton Moore, explained why the lab power supplies that were used, Perini & Scott 30V 2A, were the largest power supplies given their modest capability.

He explained that they were almost student proof. He went on the classify students in three categories, the average students constituted the bulk, then there were the quite inept who damaged the best equipment by doing things that no one could have anticipated, and the very bright who sought to understand equipment and expose their weakness.

Milton explained that they tested these power supplies using the rat tail file and hacksaw blade test. One output terminal was attached to the rat tail file and the other to a hacksaw blade, the voltage and current were set to max and the rat tail file and hacksaw blade were rubbed together yielding a shower of sparks… and possibly smoke from the DUT.

At the time I was very interested in overcurrent protection of linear regulators, so this was especially interesting.

ua723 – the darling of power supply designers of the time

Lets look at the issue with the ua723, recently released at that time and appearing in lots of designs.

Above is a schematic from the ua723 datasheet. Rsc is the current sense resistor and it is chosen to develop 0.6V at the current limit, so for instance in a 20A power supply it would have a value of 0.6/20=0.03Ω. So, the current sense circuit presents a Thevenin equivalent circuit of Vth=Rsc*I and Rth=Rsc. Continue reading Milton Moore’s power supply test

Current regulation dynamics of Atten APS3005S

This article documents a simple test to ascertain whether the current regulation dynamics of are good enough to use for testing strings of LEDs as found in much modern lighting


The APS3005S is a linear bench top power supply 0-30VDC at 0-5A with adjustable voltage and current regulation… so called constant voltage and constant current modes.

A pair of 900mm long small gauge (0.5mm^2) hook up leads were used to apply a short circuit to the power supply, and current was set to 0.1A. The resistance and inductance of these leads will to some extent limit the peak current.

The short circuit was removed and the power supply set to 30V out.

The short was reapplied and the current captured with a current probe. The current probe calibration is 1mV/10mA.

Above, the peak current is 6680*0.1=66.8A, that is 668 times the set value. Continue reading Current regulation dynamics of Atten APS3005S