A Silicon-Based LED Packaging Module With a Temperature-Dependent Capacitor for Constant Voltage Control

Abstract

Since LEDs have a voltage drop specified at the intended driving current, a power source with constant current control is desirable in order to produce a stable illumination. However, this approach requires complex electronic components for power signal processing; this would increase the cost and decrease the reliability of the LED module. As a result, a silicon-based LED packaging module with a thermosensitive capacitor is proposed in this paper; it is meant to achieve electrical self-compensation and deliver a stable current to the LED under a constant voltage control mode. The packaging module uses a 3-D stacking technology to integrate the LED and a solid capacitor on a silicon micromachined substrate. A specific inductor was connected to the capacitor for electrical impedance when a constant voltage with a periodical switch mode is applied to the LED. Based on this configuration, the temperature generated by the LED can directly change the capacitance in a series circuit, thereby compensating for the resistance variation of the LED to produce a stable driving current. The electrical compensation performance for specified ceramic capacitors was evaluated using the Multisim software and via experiments. The results show that the variation in temperature-dependence capacitance under a constant voltage control mode can effectively prevent the LED current from rapidly increasing, resulting from increased temperature. For a typical packaging module with a thermosensitive ceramic capacitor, an LED driving current of 0.4 A can be achieved at a constant supply voltage of 8 V, while the corresponding LED temperature is $\sim 120^{\circ }\text{C}$ .