Identifying 4 terminal device on LED panel

[genericpurpleturtle]

Hello everyone, I've got this little LED PCB panel thing which has fifteen LEDs on it, three 0 ohm resistors and three 4 legged devices (circled in red the picture). I have no idea what the little 4 legged devices are though, or what their purpose is and was wondering if anyone had any ideas?

I've tried googling the markings on the device with no luck; I think it says WGS71, where the S has a little line over the top of it and the 71 is at a 90 degree angle to the rest of the text.

The only information about their behavior  which may be of use that I have is that, I think the PCB is meant to be powered by 24V (not sure though, they were given to me without packaging), and if you gradually ramp up the voltage from 0V, first the 9 LEDs which I have circled in green come on dimly at about 8V and then become brighter. The last 6 only come on at about 13V, again dimly at first, then brighter.



The reason I want to know, is that I'm trying to set up a an experiment where I drive the LED panel with a sinusoidal signal to find out what frequencies of flashing light at visible. I was going to use a op amp in a transconductive configuration decribed here:
( http://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/voltage-to-current-signal-conversion/ ) to convert a voltage signal from my signal generator into a current one. I wanted to know if these little 4 legged devices would cause unexpected behavior in the panel.

Many thanks for any and all help

[Ondre]

Hi,
the package is a SOT143 or TO253. Digikey spits out some bridge rectifier with this package type. You could try to remove one from the circuit and check if they are diodes inside. The traces are a bit hard to recognize on the photo. Maybe you can try to draw the circuit diagram to see what's connected to what.
Cheers

[bktemp]

BCR402R: 20mA LED driver. Marking code is W6s and package is SOT143

[orolo]

From the layout, you have three identical led strings. Each string is LED-R0-LED-LED-SOT143-LED-LED. The last two leds in each string are the last to turn on in your circuit. That suggests your mistery component is a resistive shunt: http://www.farnell.com/datasheets/39875.pdf something like this.