I am trying to implement the schematic found on the datasheet for it’s trailing edge dimming capabilities. Below is the schematic I have assembled for the PCB.
I cannot seem to get an output on the load side. I think I have narrowed it down to the voltage supply to the IC, but I not sure what I am doing wrong. Below I have added some of the key waveforms. Channel 1 is the node connected to R150k and R30k after the diode. Channel 2 is the VDD pin. Channel 3 is the VS pin. Channel 4 is the DRVGate pin.
It seems like it is half-wave rectifying like expected, but the source pin is not regulating at 17V and is sitting at about 7V. I assume this is also causing the VDD pin to have those strange fluctuations with a max at about 2.5V. I am also not sure why the gate drive pin looks like that or why it cannot be controlled with the potentiometers, but I am assuming that it is all a supply voltage issue.
@matthew.payne
Can you confirm the exact voltage you are supplying to the FL5160MX?
The input to the board is 120Vrms. Based on my understanding of the given schematic, this should be half-wave rectified by D1, filtered by C4.7u, and internally clamped to 17V. However, with the given schematic, a scope measurement of the VS pin is reading an average of about 7V.
@Nathan_2268
I got the leading edge system to work as expected based on the updated schematic below. Adding diode D2 to get another half cycle and reducing R30k to R7.5k seemed to fix the input power issue. However, I still cannot operate the IC as trailing edge. When I pull DimMode to ground, DRVGate falls to zero and no longer drives the FETs. Any idea what the issue might be?
Hi matthew.payne,
I’m not certain what’s going on with your circuit at the moment, but I’d do a few things to start debugging it.
- Triple check all connections for bridges and cold solder joints.
- Be absolutely certain that your PCB actually matches the schematic.
- Verify that your POTLEAD potentiometer (Radj in Fig.4 of datasheet) is a 250k pot connected in rheostat mode (wiper tied to one end terminal).
- Make sure no parts have been damaged.
- Double check that the pinouts of the transistors are matching your layout and that the orientation of the FL5160 and D1 are correct. Don’t assume the pinout of any transistor. Verify with the respective datasheets.
- Verify that the values of your passive components are correct.
The datasheet does not mention what value to use for Roffset in Fig.4 (R1 for your particular circuit) but it suggests 50k for most of the other example circuits. I see you are using 250k, but I’m not clear what the purpose of Roffset is in the circuit. If the text references it, I missed it. If one could just go with zero Ohms for Roffset, then you could just short your “POTLEAD1 Pad” to “POTLEAD2 Pad” and use your 250k R1 for Radj, as that would be the same as setting Roffset to zero Ohms.
