How to drive the LED lamp string? Opens a new way for resonant control

The engineers are very clear, in mechanical and electrical systems, with the resonance or near resonance operation, it is important to the relationship between power and frequency (Figure 1). Sometimes the resonance is a bad thing, if too much energy into a single mode, may damage the system. But the resonance can be good. The resonance usually used for regulating the frequency, through the maintenance of sufficient power to keep the system oscillation resonant frequency (e.g., mechanical and electrical clock). Many people may not know, the resonance can be used to adjust the power, power can be adjusted to the variable size array of variable load. For example, the lighting array can be used in applications such as LED, to achieve solid-state lighting (SSL) system is cost effective and reliable.

Figure 1. the graph depicts a typical resonance (center frequency of 30 kHz and 20 kHz bandwidth of the normalized power). Note that the frequency of non overlapping lines.

The LED application is particularly interesting, because LED has economic significance in lighting applications is bigger, and the conventional DC driver cost and reliability problems. LED is a low voltage DC device inherent, in some point, the current voltage (I-V) curve is very steep. Although you can use the constant voltage source to drive the LED, but in fact most designers with constant current DC driver design. In order to be closer to the level in the typical distribution (e.g. 120/240 VAC) to work, usually to configure many LED lamp string lamp. The LED must be closely matched, because the current flowing through the lamp light output and each LED string is proportional to the. The failure of a single LED (such as short circuit or wiring fault) fault may cause the whole lamp string.

Distributed reactance element

The use of power to control the resonant LED array, to overcome these shortcomings of the AC LED drive. In the simplest case, the resonance can be used to control the power of a single load. Verdi Semiconductor, the effective use of the resonance, produce a current driver for LED lamp string of less components, high efficiency.

However, a more robust approach is the reactance devices distributed in array. In this way, the overall power can not only control the lighting element, and in a large network, also do not need a separate regulator of semiconductor devices to add network. The distributed reactance components of high efficiency and low cost to realize the new strong control ability. Usually, reactance element is a capacitor or inductor. In kHz to MHz frequency (or even GHz frequency, if necessary), suitable components are very small and cheap, and can be implemented as a discrete device or sheet. Specifically, we assume that the capacitors are distributed across a network, and use the discrete inductor less number, but also can make the design of inductors of low cost.

Add a series and parallel reactance components (capacitors and / or inductor) can open up a new power control method. Reactance element can form a resonant circuit, which is the main dissipation mechanism of resistive load LED. At the same time, the resistance is close to lossless reactance can replace the energy consumption, the resistance in the circuit is usually used as a current regulator in the DC drive LED the most simple.

Element and array

Imagine a lighting network composed of a group of lighting units, each of which contains one or more lighting elements, such as a pair of anode connected with the cathode of LED, and the series and parallel capacitor. The topology has many variations, but figure 2 shows a basic lighting design unit. Any quantity of the unit and the unit actual mixed topology, can be in series and / or parallel connection, formed by the series reactance resonant network consisting of. More generally, we will be the series reactance network composed of known as the "solid state lighting series reactance" (RSSL).

Figure 2. shows the two series reactance unit circuit

For example, in Figure 3, a storage circuit consists of 10 series reactance. Assume that all LED are of the same type, and all capacitors have the same value of C. The total capacitance of each unit is 2C. The total capacitance for C/5 lamp string. The resonant frequency is V (5LC). A unit of reactance is 1/2 C. As long as X? R, where R is the actual resistance of LED, while the series reactance showed pure reactance, which is equivalent to the requirements of the resonant circuit insufficient damping, Q 1?.

Fig. 3. circuit consists of 10 A unit.

You can use the circuit simulator, a detailed analysis on the specific resonant network, but also can easily be roughly estimated, the choice of components of the numerical approximate. For a given frequency, the relationship between the inductance and the capacitance is determined by the. Should choose the capacitance and reactance is large enough to ensure that the Q resonance is high enough. The current flowing through each unit is assigned to the bypass capacitor in parallel with the LED, and by a series capacitor current limiting, the effect is very similar to the current control resistor in circuit. The reactance of only using Ohm's law, we can find the desired value. Note that the bypass capacitor is not current flowing through the LED, local storage recycling current. In fact, in addition to the resonant control of the current through the lamp string, in fact there are local resonance for each LED current control.

Multiple channel and line frequency suppression

Although you can use the same capacitance value in a single frequency down the operation of the RSSL system, but do not have to do so. In fact, we can take the bus as a double lighting support spectrum contains a lot of available channels. Because no one responds to the reactance on frequency band, as long as they are in the band