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HV9910NG Datasheet(PDF) 6 Page - Supertex, Inc |
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HV9910NG Datasheet(HTML) 6 Page - Supertex, Inc |
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6 / 11 page  HV9910 6 C110504 Inductor Design Referring to the Typical Application Circuit below the value can be calculated from the desired peak- to-peak LED ripple current in the inductor. Typically, such ripple current is selected to be 30% of the nominal LED current. In the example given here, the nominal current ILED is 350mA. The next step is determining the total voltage drop across the LED string. For example, when the string consists of 10 High-Brightness LEDs and each diode has a forward voltage drop of 3.0V at its nominal current; the total LED voltage VLEDS is 30V. Knowing the nominal rectified input voltage VIN=120V*1.41=169V, the switching duty ratio can be determined, as: D= VLEDs /VIN=30/169=0.177 Then, given the switching frequency, in this example fosc=50KHz, the required on-time of the MOSFET transistor can be calculated: Ton=D/fosc=3.5 microsecond The required value of the inductor is given by: L = (Vin - VLEDs) * Ton/(0.3 * ILED) = 4.6mH Input Bulk Capacitor An input filter capacitor should be designed to hold the rectified AC voltage above twice the LED string voltage throughout the AC line cycle. Assuming 15% relative voltage ripple across the capacitor, a simplified formula for the minimum value of the bulk input capacitor is given by: Cmin = ILED*VLEDs*0.06/VIN^2 Cmin = 22 µF, a value 22uF/250V can be used. A passive PFC circuit at the input requires using two series connected capacitors at the place of calculated CMIN. Each of these identical capacitors should be rated for ½ of the input voltage and have twice as much capacitance. Enable The HV9910 can be turned off by pulling the PWM_D pin to ground. When disabled, the HV9910 draws quiescent current of less than 1mA. Figure 1: Typical Application Circuit 0.2 Ω AC Input 85-135V AC 68µ F, 160 V 750µΗ , LEDs BYV26B VN2224 coilcraft BUSH-2820R5B VIN VDD LD PW M_D GND RT CS GATE 0.1µ F, 250 V 0.1µ F, 250 V 1n F, 250 V 1n F, 250 V 2A, 250 V 2R NTC 1N4004 1N4004 1N4004 1N4004 HV9910 68µ F, 160 V 1N4004 1N4004 1 µF, 10V optional for PFC 220nF, 400 V LED(s) – a string of HB LEDs , 16 diodes 280 k Ω |
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