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Multi-output driver for LEDs Disclosure Number: IPCOM000008524D
Publication Date: 2002-Jun-20
Document File: 2 page(s) / 36K

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Multi‑output driver for LEDs

The new improvement is a multi‑output driver optimised for driving LEDs.

The following circuit diagram illustrates the operation principle. A single LED or a series string of LEDs is connected to each output of the driver. In the figure two series LEDs at each of the three outputs are shown. The number of LEDs and outputs may vary for each application. A single resistor in the return path of all the LEDs is used to measure the current through a LED or a series string of LEDs. In this way the multi‑output driver is able to have a constant current at its outputs in stead of having a constant voltage at its output.

The operation principle of the multi‑output driver is as follows. It draws a current through the coil from a power source by closing switch S1. After some time switch S1 is opened and switch S2a is closed. In this way energy stored in the electromagnetic field of the coil is converted into a current through the LEDs. This procedure is repeated for every individual output of driver, i.e. Sl‑S2b and Sl‑S2c. In this way the power of the source is converted into time­multiplexed currents through the LEDs.

The diode D1 together with the Zener‑diode Z1 form a clamping circuit that limits the amplitude of voltage spikes due to the switching actions. These voltage spikes could either be visible or damage the LEDs. If switch S1 is closed, then diode D1 also prevents the discharge of the capacitance formed by the individual capacitance of all the L...