LED current source IC

[ArticCynda]

Hi all,

I have a LED panel that started flickering, and I'm trying to diagnose the problem. Picture attached. The circuit is extremely simple: 220V AC is passing through a 2.2 ohm resistor into a small bridge rectifier. Varistor across the rectifier inputs, a small capacitor and 2M resistor across the rectified AC output.

The 72 LEDs are arranged in parallel in pairs, and there are 36 pairs in series. I presume the pairs are intended as a kind of "redundancy". The anode of this massive LED series string is tied to the rectified AC output of the bridge rectifier. The cathode of the string is going to the SOIC-8 packages on the right. All 4 chips are identical, are wired in parallel to each other, and each has a bias resistor of 20 ohm and 22 ohm respectively. Because they are in series with the LED string, I assume they must function as some kind of current source.

The inscription of the ICs, which are identical, is "1952-LF". I've tried to search online but had no luck finding anything.

I'm suspecting the flickering may be caused by overheating of the current regulator ICs, so I'd like to buy 2 more and populate the empty positions on the PCB to reduce the current through each of the parallel current regulators. But for that, I'll need to find them, of course.

Does anyone here have suggestions on manufacturers of such current regulator chips, perhaps point me in the right direction, or suggest pin compatible alternatives?

Many thanks in advance,

AC

 

[KlausST]

Hi,

schematic? There is a good reason why one invented it.

Klaus

 

[betwixt]

A close up picture of the ICs with the manufacturers logo would help us identify who makes it.

Count 5 across and 5 & 6 down in the LEDs and you will see the classic appearance of damaged die.

Brian.

 

[ArticCynda]

I have attached a schematic of the entire circuit. LEDs are in parallel in pairs, and 36 pairs in series. The 1952-LF drivers are in parallel to each other, 4 populated and 2 NC. Note that the double C1 designators in the schematic is not an error, it's also duplicate on the actual PCB.

Brian, I've had a close look at the ICs and can't find any logo, it only contains the text 1952-LF.

 

[dick_freebird]

There's a ton of LED string controllers. 36 would narrow the field some.
SOIC-8 takes it down to 3... all Microchip, looks like. But surely there are
others of type.

https://www.digikey.com/en/products/filter/power-management-pmic/led-drivers/745?s=N4IgjCBcpgbFoDGUBmBDANgZwKYBoQB7KAbRACYBOAFkqpAF0CAHAFyhAGVWAnASwB2AcxABfAtQAcCEMkjps%2BIqRABmSgFZKlEBI2TYG3RXKTJABlWMW7SF16CR4kBuoRos1JlwFikMtTkqqr0TCBsHNz8wmKiokA

Now flickering and other "behaviors" may be "proper" driver response to
LED string faults. Might check your situation before you go on a mission
to find something you didn't need, and a replacement will find the
environment just as objectionable.

 

[ArticCynda]

Thank you kindly for sharing your thoughts, I've had a look at the various ICs on Digikey, and the absence of inductors on the PCB narrows down the list significantly because it must be a linear topology rather than a buck/boost/SEPIC one, so filtering on SOIC-8 as package and linear regulation as topology reduces the search results to only 6 devices. Unfortunately none of them is pin compatible with my application.

I see your point regarding the flickering, so will follow Brian's advice and attempt swapping the two LEDs with damaged dies, and hope that fixes the issue. Will report back on the progress.