26 Led Array Component Identification and Failure Cause

Question

I have the following LED lights. These lights keep failing on me. I'm suspecting that the DPAK(U1) component is failing but I have no clue what it is. The markings on the DPAK reads 5ZYl8GF6D. I'm assuming it is some sort of voltage/current regulator.

How the device fails

Two devices lights are about half the brightness of a working one with a slight flicker. Also takes about twice as long to turn off fully. Third device is dead as a stone and the PCB around DPAK is discolored

Mesurments

Rectifier:

AC to V+ and V- is 0.6V drop

V+ to V- is 1.14V drop

Meter does not give me a reading on the LEDs.

The rest of the values correspond to there marked value.

The schematic is as follows

The x10 refers to 10 LEDs in series and x16 to 16 in series.

Assuming a voltage drop of 2.5V for the LEDs (White). The input voltage should be about 286Vdc to the DPAK(U1). The device claims to be 18W but I have no way I consider to be safe to test this.

I'd like to replace the DPAK with a better component or at lease keep a supply of its equivalent.

EDIT

After googling a bit more I found this.

Design LM317 Constant Current Circuits and this chip.

From what I gather the 10R resistor controls the current with Iout=Vref/R so this gives it a Iout of 120mA witch is beyond the chips ratings.

The stated 18W gives a value of 54mA as the max current witch is slightly over the limit of the chip.

Answer 1

You may be right. In my opinion U1 is a stabilizer in a current limiter configuration. U1 transmits current to the value when the voltage drop across R3 is equal to Uref U1. The marking is a bit not typical, but it can be either some rare high voltage stabilizer or some cheap Chinese stabilizer with very poor parameters.

Discoloration around the stabilizer is not surprising, because with this configuration, it will heat up strongly.

Maybe the stabilizer has overheated and is actually damaged.

If I were you, I would do that:

1. I'd check all of the diodes for damage. I would take a power supply unit with a current limiter (voltage: 3V DC, current limiter: 80 mA) and check each diode individually to see if it lights up.
2. If all diodes are on, I would try to replace U1. Theoretically you can give a normal stabilizer like LM317 (you have to check if the pad leads match). The main criterion for using the stabilizer is the voltage difference between input and output. In this case U1 is not connected to GND. So the voltage on it is a voltage drop on the stabilizer+ voltage drop on R3. Rather, it should be a small voltage value, so there is a chance that an ordinary LM317 will work in this role. But this is just theoretical considerations and don't take it for granted. Be careful!

Answer 2

Replaced the DPAK (5ZYl8GF6D) with a LR8. The light is dimmer but usable now.

I picked the LR8 because in the functional block diagram it has builtin over-current and overheat protection built into the chip as well as the high input voltage. The high input voltage might not be required as @sigaris mentions but I was not willing to measure on live connected device to get the actual voltage drop.

This is rectified mains voltage. NEVER work on a device like this with power connected.