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HV9922 Datasheet(PDF) 7 Page - Supertex, Inc |
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HV9922 Datasheet(HTML) 7 Page - Supertex, Inc |
7 / 10 page HV9921/22 NR040805 7 switching currents of the converter. As a rule of thumb, this capacitor should be approximately 0.1- 0.2 µF/W of LED output power. A recommended input filter is shown in Figure 2 for the following design example. Design Example 1 Let us design an HV9921 LED lamp driver meeting the following specifications: Input: Universal AC, 85-264VAC Output Current: 20mA Load: String of 10 LED (LW541C by OSRAM VF = 4.1V max. each) Step 1. Calculating L1. The output voltage VO = 10 ⋅ VF ≈ 41V (max.). Use equation (1) assuming a 30% peak-to-peak ripple. mH mA s V L 72 20 3 . 0 5 . 10 41 1 = ⋅ ⋅ = µ Select L1 68mH, I=30mA. Typical SRF=170KHz. Calculate the coil capacitance. pF KHz mH SRF L C L 13 ) 170 2 ( 68 1 ) 2 ( 1 1 2 2 ≈ ⋅ ⋅ = ⋅ ⋅ = π π Step 2. Selecting D1 Usually, the reverse recovery characteristics of ultra- fast rectifiers at IF=20~50mA are not provided in the manufacturer’s data books. The designer may want to experiment with different diodes to achieve the best result. Select D1 MUR160 with VR = 600V, trr ≈ 20ns (IF=20mA, IRR=100mA) and CJ ≈ 8pF (VF>50V). Step 3. Calculating total parasitic capacitance using (3) pF pF pF pF pF C P 31 8 13 5 5 = + + + = Step 4. Calculating the leading edge spike duration using (4), (5) ) ( 136 20 100 31 2 264 MIN BLANK SPIKE T ns ns mA pF V T < ≈ + ⋅ ⋅ = Step 5. Estimating power dissipation in HV9921 at 264VAC using (8) and (10) Let us assume that the overall efficiency η = 0.7. Switching power loss: () ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ ⋅ + ⋅ ⋅ ≈ 7 . 0 41 264 20 100 2 31 264 5 . 10 2 1 V V ns mA pF V s P SWITCH µ mW P SWITCH 120 ≈ Minimum duty ratio: 16 . 0 ) 2 264 7 . 0 /( 41 ≈ ⋅ ⋅ = V V D m Conduction power loss: ( ) mW V A mA P COND 55 264 200 63 . 0 210 20 25 . 0 2 ≈ ⋅ ⋅ + Ω ⋅ ⋅ = µ Total power dissipation in HV9921: mW mW mW P TOTAL 175 55 120 = + = Step 6. Selecting input capacitor CIN mW mA V 820 20 41 Power Output = ⋅ = Select CIN ECQ-E4104KF by Panasonic (0.1µF, 400V, Metalized Polyester Film). Design Example 2 Let us design an LED lamp driver using the HV9922 that would meet the following specifications: Input: Universal AC, 85-135VAC Output Current: 50mA Load: String of 12 LED (Power TOPLED ® by OSRAM, VF = 2.5V max. each) Step 1. Calculating L1. The output voltage VO = 12 ⋅ VF = 30V (max.). Use equation (1) assuming a 30% peak-to-peak ripple. mH mA s V L 21 50 3 . 0 5 . 10 30 1 = ⋅ ⋅ = µ Select L1 22mH, I=60mA. Typical SRF=270KHz. Calculate the coil capacitance. pF KHz mH SRF L C L 15 ) 270 2 ( 22 1 ) 2 ( 1 1 2 2 ≈ ⋅ ⋅ = ⋅ ⋅ = π π Step 2. Selecting D1 Select D1 MUR160 with VR = 600V, trr ≈ 50ns and CJ ≈ 8pF (VF>50V). |
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