SOLVED Unmarked Component Identification Help

[wraper]

Yes I did measure the gate voltage being applied that way. I assumed that was how much MOSFET required to turn on.

There is no DC, gate is switched at very high frequency. You cannot measure that with multimeter.

[ajp8868]

Ah ok, so input to the board is 12v from a separate smps, there is only one LED on the output of each channel and there are 4 LEDs on the single chip, so 4 channels. There's 4 identical coils/ICs in a row.

[wraper]

IMHO use 40-60V N-channel MOSFET with 8-15A current rating, low RDSon, say below 80 mOhm and you should be safe. 5A MOSFET will work too but there will be more heat dissipation. And I have no idea how good is heat transfer on that board. Do not go into too high current rating since gate charge will increase and will become harder to drive for controller IC.
For example RSD080N06TL or STD46N6F7

[ajp8868]

Brilliant, thank you for your advice. I'll get one ordered and update you once it's back together!

[fzabkar]

The current for the LED is set at around 5A (= 250mV / 46 mOhm).

Vcs = 250mV
current sense resistor = 46 mOhm

Assuming that each LED drops around 3V, then the power rating for all 4 LEDs would be 60W (= 4 x 3V x 5A). That matches the specs in my searches.

I'm wondering whether the dissimilar current sense resistors allow for slightly different currents for each colour, perhaps for balancing the intensity?

[ajp8868]

That all sounds correct, the light is supposedly 60w and the max current tested on the datasheet is 4.5a.

Just a bit of a noob question, but how does the current sensing drop to 250mv? I thought the drain would be connected to the source once the MOSFET was turned on, causing that area of the board to be around 10v? Or does the coil drop that?

[fzabkar]

Look at the application circuit in the datasheet. The current in the sense resistors is sensed via the Vcs pin. The converter regulates the current by monitoring this pin and maintaining a voltage of 250mV (as per the spec).

BTW, does each LED have a different combination of sense resistors?

[ajp8868]

Ahh that makes sense, thank you for explaining. They all have the same set of 3 resistors.

[ajp8868]

Thanks very much for the help guys, that MOSFET worked like a charm and I now understand the theory behind it much better!

Cheers