1.3 Top Side Pump

Currently LED systems are designed for a lumens level below 2000 when using the standard three channel architecture where one color (Red, green or blue) would be used per channel. As shown in Figure 3, there exists a limitation from the system étendue, meaning that it is not possible increase the lumens by simply making the light emitter larger while maintaining the size of the imager (DMD) constant. This is where a new innovative concept called Top Side Pump (TSP) comes in, allowing for higher lumens with the use of a 4th LED in the system.

To produce a green light, manufactures take a blue LED and use a green phosphor layer to convert the blue spectrum light into green. As shown in Figure 4, TSP takes advantage of this concept by adding an additional blue LED to further excite the top side of the green phosphor to have a greater green output. The result is about an enhancement of 40%, but to maintain the white point, this translates to approximately a 15% boost in lumens. The limiting factor for TSP is the red channel LED, if more red was produced, then more of the available green output could be used.

Green LED requires driving 2 diodes: Green LED and Blue pump LED together. With that in mind, here are the real voltages that are supplied for the driver to accommodate Green and Blue pump LED now requires 31.6 V to driver both diodes in series.