Design Idea DI-66 (R) TOPSwitch-GX 45 W, Universal Input, LCD Monitor Internal Supply Application Device Power Output Input Voltage Output Voltage Topology LCD Monitor TOP246Y/F 45 W 90-265 VAC 5 V / 12 V Flyback The switching frequency of U1 is set to 66 kHz by connecting its F pin to the CONTROL pin. Efficient 66 kHz operation results from the use of an EER3016S core to keep the number of primary turns low and to further reduce T1 leakage inductance. This reduces the losses due to both leakage inductance and winding capacitance. Low leakage inductance also allows the use of a low cost RCD snubber (C3, R2-R4 and D5) to clamp the U1 DRAIN voltage, while keeping standby power consumption low. Use of a glass-passivated normal recovery diode (D5) recycles the stored leakage energy and increases the overall efficiency. Resistor R4 dampens drain node ringing, and is necessary when a normal recovery diode is used. Design Highlights * 66 kHz operation enables 0.45 W of standby output power delivery with 0.9 W of input power at 230 VAC * Low no-load input power: <0.42 W at 230 VAC * 82% efficient (min) at 90 VAC input and 45 W output * Low component count: only 52 parts! * Meets CISPR22 B EMI with > 10 dB of margin * No TVS required for the primary snubber Operation Many of the built-in features of TOPSwitch-GX, such as line UV/OV, soft start, line feed-forward, accurate current limit, and frequency jitter have been used to reduce the component count, transformer size and overall system cost of this universal input, flyback power supply. This design is ideal for LCD monitor supplies that require low standby power consumption. C3 10n 1 kV R2 68 k 1/2 W NEUT 90-265 VAC LINE F1 3.15 A 250 V RT1 5/3 A 2 C1 100 F 400 V L2 3.3 uH 10 D12 MBR20100CT C9 680 F 16 V C10 680 F 16 V 6,7 R6 7.5M 1/2 W L1 5.3 mH 1A CY2 330 pF Y1 5 D5 1N4007G CY1 330 pF Y1 CX1 330 nF X2 CY3 2.2 nF T1 R12 C8 68 470 pF R5 2M 1/2 W D1-D4 RL205 GND 1 R4 10 1/2 W R3 68 k 1/2 W R2 2M 1/2 W Resistor R5 sets nominal UV and OV limits to 84 V and 378 V, respectively. Under-voltage lockout protects the supply from overheating during brownout, and eliminates power-up and power-down glitches. Overvoltage shutdown protects the power supply from line surges. R13 390 C13 680 F 10 V 5 V/1.8 A C14 100 F 25 V R14 22 RTN 8,9 TOPSwitch-GX U1 TOP246Y 3 L D CONTROL D10 LL4148 4 C S L3 3.3 uH C11 100 F 25 V C15 330 nF C12 680 F 10 V D13 SB540 12 V/ 3 A C6 47 F 50 V R15 1.0 k U2 PC817C X F R7 7.87 k R8 6.8 C4 100 nF R9 330 C5 47F 10 V L4 6 x 5 mm Bead Ferrite C16 47 nF R16 10.0 k R17 2.2 k C17 10 F 35 V U3 LM431AIM3 R18 10.0 k PI-3743-120904 Figure 1. Circuit Diagram of a TOP246 Based LCD Monitor Power Supply. DI-66 www.powerint.com December 2004 DI-66 Effective EMI filtering is accomplished with only five parts (L1, CX1, CY1-CY3), due to the built-in frequency jitter function of TOPSwitch-GX. TRANSFORMER PARAMETERS Samwha EER3016S-PL-7 ALG of 342 nH/T2 Core Key Design Points 10 Pin, EER3016S Bobbin * Use 66 kHz operation to reduce standby power loss. * To reduce the number of primary turns required for 66 kHz operation, the Ae of the T1 core must be large. Recommended cores are EER3016S and PQ2620. * Split-primary transformer construction should be used to keep leakage inductance to a minimum. * Use an RCD snubber with the normal recovery diode. Size resistors R2 and R3 for the highest value that ensures adequate drain voltage margin under overload conditions at high line. Winding Details 1/2 Primary: 28 T, 26 AWG Bias: 7T, 2 x 26 AWG 12 V Secondary, 4T, 2 x 25 AWG Triple Insulated Wire 5 V Secondary: 3T, 3 x 25 AWG Triple Insulated Wire 1/2 Primary: 24T, 26 AWG Winding Order (pin numbers) 1/2 Primary: 2-5, tape 1L Bias: 3-4, tape 2L 12 V Secondary: 10-6,7 5 V Secondary: 6,7-8,9, tape 2L 1/2 Primary: 5-1, tape 3L Primary Inductance 919 H 10% Primary Resonant Frequency 1.1 MHz (Min) 18 H (Max) Leakage Inductance 70 (QP) (AV) 50 1.1 1 Input Power (W) Amplitude (dBV) 60 1.2 40 30 20 10 Quasi-Peak Scan PI-3744-102403 80 PI-3745-102403 Table 1. Transformer Construction Information. 0.9 0.8 0.7 0.6 230 VAC 115 VAC 0.5 0.4 0 Average Scan -10 0.3 0.2 -20 0.15 1 10 0 70 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Output Power (W) Frequency (MHz) Figure 2. Conducted EMI, CISPR22B Limits, Maximum Load, Secondary Return Connected to Safety Ground, 230 VAC Input. Figure 3. Pin vs. Pout, 5 V Output Loaded, No Load on 12 V Output. 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