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AB171 Datenblatt(PDF) 9 Page - Lumileds Lighting Company |
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AB171 Datenblatt(HTML) 9 Page - Lumileds Lighting Company |
9 / 13 page AB171 LUXEON SunPlus 35 Line for Horticulture Application Brief 20161110 ©2016 Lumileds Holding B.V. All rights reserved. 9 7.2 Active Control LED Current Driver There are two types of active control LED current drivers: – Linear regulated power supply – Switch mode power supply The main difference is how the power supply is being regulated. In linear regulated power supply, the transistor connected to a load is used to control the output voltage or current. In order to do this, the transistor must operate in the ohmic or linear region as shown in Figure 6. Since there is current flowing through the transistor (operating in ohmic region), the transistor behaves like a variable resistor and generates heat. In a switched mode power supply, as the name implies, the transistor is used as a switch to either switch in or out electrical storage elements such as inductor (current source) or capacitor (voltage source) to a load. In order to achieve this, the transistor must be operating in the saturation region as shown in Figure 6. In the “ON” or close switch, there is hardly any resistance through the transistor and hence does not generate any heat when a current flows through it. In “OFF” or open switch, no current is flowing through the transistor. This type of power supply has high power efficiency than the linear regulated power supply. However due to the switching of the circuit, it generates electromagnetic interference (EMI) which must be taken into account and minimized during the design stage. There are several switch mode power supply configurations such as buck, boost and buck-boost convertor. Figure 6. Typical transistor operation regions. Ohmic or linear region is shaded in yellow while the saturation or switching region is shaded green. A summary of the major differences between these two active control LED current drivers is given in Table 3 below. Table 3. Comparison of a typical linear regulated versus switch mode power supply. LINEAR SWITCH MODE Cost Cheap Expensive EMC None Potential Circuitry Simple Complicated Power Efficiency Low (~50...~70%) High (~75%...~95%) Size and Weight Big and heavy 1 Small and light Notes for Table 3: 1. If magnetics are used to step down the voltage before the regulator. |
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