Can anyone identify this chip

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Can anyone identify this chip

Postby Mjolinor » April 13th, 2016, 11:11 am

I have these LED lights and they have ceased to function.

http://www.ebay.co.uk/itm/42-240W-80-Le ... Sw2GlXDkt5

Mine have 42 leds @ 3 watt.

I have drawn out the circuit but the chips have no numbers on them. I figure they are some sort of voltage regulator feeding a PWM to the LEDs but I cannot match any that I know. (XL1410, MC34063, FM6316).

The circle is actually two transistors in parallel. There are 12 LEDs, 4 strings of 3 in series (only one shown because I am lazy)

My circuit tracing abilities are similar to a moose's abilities to do calculus so if you know something that nearly fits it is probably correct.
Attachments
1.jpg
2.jpg
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Re: Can anyone identify this chip

Postby Mjolinor » April 16th, 2016, 8:46 am

OK. I drew the circuit out.

Image

What i think is happening:

D2 is protection against reverse polarity
D1 is protection from collapsing magnetic field of L1

That leaves the 8 pin DIL with power in on pin 5 or 6 and ground on pin 3.

Pin 4 is an output and pin 2 is measuring the voltage across the resistor R 4/5

Q 1/2 is (I suspect) a P channel MOSFET.

Pin 4 goes low, voltage across transistor goes to 0, voltage across R 4/5 starts to rise, pin2 is an analogue input and once a certain threshold is reached pin4 goes high and the whole thing free runs like that.

So if that is how it works then no need for voltage / current regulation and the DIL is a PIC or similar. the 56 k is pulling up a reset line I reckon.

Any better ideas?

Would the base (gate) of the transistor ever get high enough for the thing to switch off. Maybe this is why it blew, there should be a pull up. Chinese corner cutting?
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Re: Can anyone identify this chip

Postby bandersnatch » April 16th, 2016, 4:37 pm

Hi,

Nobody else has responded yet, so here's my 10 cents...

I initially figured that you were right in assuming some sort of PWM driver chip until I did a bit of digging in the net.
I searched for "led spotlight driver circuits" "led power driver circuits" & checked out the images containing ICs with 8 pins..

I was surprised (& somewhat dismayed ;^) ) at the huge variety of different driver applications and circuits....
In addition to PWM drivers, there are current sense drivers, buck drivers, array drivers etc. etc. etc...

After many fruitless red herrings I DID find a circuit that at least seems to use the same pins of an 8 pin IC in a similar
circuit configuration.
Check out: http://www.diodes.com/_files/product_ap ... N75_r0.pdf
This is an "AL9910 high power factor buck LED driver"
The circuit in the green box on page 1 looks VERY similar to your circuit.
If your circuit is also a buck converter then this would also explain why the circuit seems a bit wierd & not easy to understand..

I dunno if this will help, but this is the only circuit I found that is close to your device & the "high power factor 13W LED lamp"
application also matches your device....

Just in case you don't already know them, here are a few tricks for reading illegible/invisible IC markings..
1/ Use a bright light and magnifying glass to examine the chip at all possible angles (especially at very low angles, almost from the side)
2/ Repeat step 1/ with a UV light source
3/ Wet your finger & rub a thin film of moisture on the chip & repeat step 1/ as it dries
4/ Spray a thin film of contact cleaner on the chip & repeat step 1/ as it evaporates
5/ Spray a thin film of freeze spray on the chip & repeat step 1/
6/ Cool (dont freeze!) the pcb in a fridge, then breathe on the chip & repeat step 1/
7/ Desolder the sucker & look underneath

If you have'nt already tried all the above then give it a go.
I have often been amazed how "invisible" markings can be revealed by the above methods.

I hope this helps you with your puzzle.

Irrelevant mythological quote: "Be yourself, unless you can be Loki, then be Loki"
STFB
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Re: Can anyone identify this chip

Postby Mjolinor » April 17th, 2016, 4:15 am

Excellent. That is so similar it has to be right. This thing will run from 12 to 24 votls so I would expect a chip of this sort.

The problem now is that for sure pins 1 and 7 go nowhere on my board. From the datasheet I think it may be possible for pin 1 not to be connected but pin 7 seems to be needed I think.

I will read the datasheet and see if I can overcome these things but I think it has to be the right chip, they jsut do not come that similar and not be right.

The numbers are so seriously removed that the chip is thin, I bet on some they actually go through while removing it. I have tried all the dip it in alcohol, view from where ever angle and so on all to no avail.

I have asked hte manufacturer for the chip number too but there is not much chance of that happening.
Thanks for the input.
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Re: Can anyone identify this chip

Postby Mjolinor » December 16th, 2016, 8:38 am

Just an update. You were right with the chip, ordered off ali-express and replaced the transistors (N channel) too and they are back alive now.

Cheers for the suggestion.
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Re: Can anyone identify this chip

Postby bandersnatch » December 16th, 2016, 2:02 pm

Kool!!!!!

Thanx & praise for a number of reasons.

Thanx...
4 the update. :^)))
It's always nice to know when a suggestion actually leads somewhere.

Praise....
For sticking with it & not just throwing the unit onto the ever increasing piles of electronic junk in this world.
Your other forum contributions indicate that you are not short of projects & your time is precious.
The unit in itself is probably not really worth much more than the time we have both spent but I salute
your readiness to even consider repairing something that most others would just throw away.
IMHO, electronic resurrection performed out of principle/curiosity is also in the spirit of hacking.....

I hope you got a nice buzz from your success & I look forward to your next puzzle ;^)
STFB
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Re: Can anyone identify this chip

Postby Mjolinor » December 17th, 2016, 7:08 am

You are right with the time / cost of repair. It is possible to buy new for much much less than the time and money I put into it.

There is another reason for doing this, once I had the chip type I am now going to see how hard I can hit the LEDs with an ESP8266 for the enable signal in order to obtain a seriously bright flash in very short time, fifty or so microsecond sort of pulse lengths, the sticking point right now is that sense resistors are horribly expensive for what they are so I am trawling Ali-Express for low resistance value sets (< 0.5 ohm). Some datasheets say that max current is as stated but some say you can hit them with very high currents provided the average allows the heat to be dissipated in time. I have several boxes of new Luxeon 3 watt that are ideal for such messing.
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Re: Can anyone identify this chip

Postby bandersnatch » December 18th, 2016, 3:52 am

HI,

.. Old school hacking suggestion...

Have you considered building your own low-value resistors using nichrome wire?
You can get any high-power low-value resistance you want by trimming the wire to the right length.
If you dont have a low-ohm mulimeter you can quickly knock up a wheatstone bridge for accurate measurement..
You can wrap the wire around a cheap high-value resisor for stability/mounting purposes.

I also suggest you experiment with extra heatsinks when pushing the power limits.
Regardless of whether or not the lights are designed for extra heatsinks, adding extra thermal dissipation
(heatsink+thermal conduction paste+fan etc.) will allow you to push the limits further

Send us some pics if you manage to spectacularly fry any lamps ;^)))))

STFB
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Re: Can anyone identify this chip

Postby Mjolinor » December 19th, 2016, 2:31 am

I am using Nichrome at the moment. Connecting to it is horrible to get reliable and repeatable so I use small crimp weight things that fishermen use for something (I know not what) but they are perfect for connecting Nichrome to copper.

I have been doing some calculations to try to reach the numbers that a xenon tube will give and it's looking like several thousands amps. I can't see this working. :)
Mjolinor
 
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Location: Burnley, UK


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