Hi Folks
This has to do with a LED light driver rated for Output - DC36-65V 300mA. This is used to drive a 15W LED panel light.
Now this does not work so opened up and found 2 resistors burnt to crisp. Sensing a learning moment, i looked around the circuit to figure out that it is built around the OB2538 chip. The circuit to a large extent follows the sample application circuit mentioned in the data sheet. I have traced the actual circuit and the same is also attached for reference.
But i have some queries on this circuit
1. The resistors that burnt to crisp are the ones connected to the Current Sensing Input of the chip. in the data sheet sample application circuit there is only one resistor from current Sense Input of the chip to the common. But in the actual PCB, i noticed that instead of one resistor they have used 2 resistors in parallel (22 Ohm and 1.1 Ohm) and these are the 2 resistors that have burnt out. I got the values from similar LED driver in another light. So why would they replace a single resistor with 2 resistors in parallel and that too with such varied values (22 Ohm and 1.1 Ohm). Further if i look at the PCB Layout, it would seem that the original design was to have the parallel resistors next to each other on the board. If you look R3A and R3B. But R3B is not populated instead what they did was put the second resistor on the back side of the board (R7). Would this be to better handle dissipation of heat from these resistors ?
2. Can a input power surge cause only these 2 resistors to burn out considering there a fuse resistor at the ac input, or is this a failure of the OB2538 chip?
This has to do with a LED light driver rated for Output - DC36-65V 300mA. This is used to drive a 15W LED panel light.
Now this does not work so opened up and found 2 resistors burnt to crisp. Sensing a learning moment, i looked around the circuit to figure out that it is built around the OB2538 chip. The circuit to a large extent follows the sample application circuit mentioned in the data sheet. I have traced the actual circuit and the same is also attached for reference.
But i have some queries on this circuit
1. The resistors that burnt to crisp are the ones connected to the Current Sensing Input of the chip. in the data sheet sample application circuit there is only one resistor from current Sense Input of the chip to the common. But in the actual PCB, i noticed that instead of one resistor they have used 2 resistors in parallel (22 Ohm and 1.1 Ohm) and these are the 2 resistors that have burnt out. I got the values from similar LED driver in another light. So why would they replace a single resistor with 2 resistors in parallel and that too with such varied values (22 Ohm and 1.1 Ohm). Further if i look at the PCB Layout, it would seem that the original design was to have the parallel resistors next to each other on the board. If you look R3A and R3B. But R3B is not populated instead what they did was put the second resistor on the back side of the board (R7). Would this be to better handle dissipation of heat from these resistors ?
2. Can a input power surge cause only these 2 resistors to burn out considering there a fuse resistor at the ac input, or is this a failure of the OB2538 chip?
Attached Files
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