New dimming technique

AN2042

10/30

Figure 8.

Dimming technique using series switch

To overcome this problem, a patented solution has been implemented, which allows to

eliminate the series switch, with a considerable improvement in terms of efficiency.

The new technique consists in a double control loop: a current and a voltage control loops.

The first one drives the LEDs with constant current when the maximum luminosity is

required. During the dimming operation, the current control loop will still limit the maximum

output current, while the voltage loop will maintain the output voltage below the threshold

voltage of the LEDs array. Also disconnecting the LEDs, the maximum output voltage will be

limited by the voltage loop. In Figure 9 and Figure 10 the block diagram of the new dimming

technique and the temporal diagrams are respectively shown. Thanks to the absence of the

power switch, it is possible to have a more efficient and cheaper solution.

Figure 9.

Dimming technique using the new methodology