® RD8 TinySwitch TM Reference Design Board 85 to 265 VAC Input, 3 W Output Low Cost Production Worthy AC Adapter Reference Design • Cost competitive with linear solutions (regulated 50/ 60 Hz transformers) • Lowest component count switching solution • Ultra low no-load power consumption (30/70 mW @115/ 230 VAC) • Simple low cost two-winding transformer • Greater than 72% efficiency • Low average EMI, only one inductive component required for EMI filtering • Small size 1.30 in. (33 mm) 1.80 in. (45 mm) 0.80 in. (20 mm) PI-2252-091098 Designed for World Wide Operation • Designed for IEC/UL safety requirements • Meets FCC/VDE Class B EMI specifications • Wide range input voltage Description The RD8 reference design board is an example of a low cost production worthy design for an AC wall adapter or similar applications requiring small size, high efficiency, and low cost. The RD8 utilizes the TNY254 member of the TinySwitch family of low cost Off-line Switchers from Power Integrations. It is intended to help TinySwitch users develop their products quickly by providing a production ready design which needs little or no modification to meet system requirements. The RD8 is designed to replace conventional linear AC wall adapters, offering universal input range, smaller size, and high efficiency, all at a competitive cost. The RD8 is cost-competitive with linear solutions (regulated 50/60 Hz transformers). The unique ON/OFF control scheme of Tinyswitch virtually eliminates energy consumption at no load. Typical linear wall adapters consume 1-4 watts at no load, which costs $1-$4 per year ( based on $0.12/kWhr). In comparison, a typical TinySwitch supply consumes 30-70 mW at no load, offering substantial energy savings. Figure 1. RD8 Board Overall Physical Dimensions. PARAMETER Input Voltage Range Input Frequency Range LIMITS 85 to 265 VAC 47 to 440 Hz Temperature Range 0 to 50°C Output Voltage (Io = 0.33 A) 9 V ± 7%* Output Power (continuous) 3W Line Regulation (85-265 VAC) ± 0.5% Load Regulation (0%-100%) ± 1% Efficiency (PO = 3 W) Standby Power Consumption (115/230 VAC) Output Ripple Voltage 72% (min) 30/70 mW (typical) ± 75 mV Safety IEC 950 / UL1950 EMI VFG243B (Quasi-Peak) VFG46 B (Average) CISPR22 B FCC Part 15 "B" * Can be improved to ± 5% by using a more accurate Zener (± 2%). Table 1. Table of Key Electrical Parameters. March 1999 RD8 L1 5 mH 3 4 R1 2.2 Ω 85-265 VAC Fusible C1 4.7 µF 400 V D5 11DQ06 L2 Bead 9 C6 330 µF 16 V R2 4.7 kΩ D3 D1 1N4005 1N4005 T1 D R4 1.5 kΩ 1/2 W C2 4.7 µF 400 V U1 TNY254P 6 TinySwitch BP +9V RTN VR1 1N5237B EN U2 LTV817 S C3 68 pF C7 100 µF 25 V C4 0.1 µF D4 D2 1N4005 1N4005 C5 2.2 nF Y1 Safety PI-2250-090398 Figure 2. Schematic Diagram of the 3 W RD8 Power Supply. R1 C1 D1 T1 D5 C6 D2 D3 L1 R2 L C2 L2 R4 D4 C5 C3 Jmp 1 N + C7 U1 C4 U2 VR1 G COMPONENT SIDE SHOWN* * Shown 1.5 X actual size PI-2254-091597 Figure 3. Component Legend for the RD8. General Circuit Description The RD8 is a low-cost flyback switching power supply using the TNY254P integrated circuit. The circuit shown in Figure 2 details a 9 V, 3 W power supply that operates from 85 to 265 VAC input voltage, suitable for replacing conventional linear supplies in cost-sensitive applications such as AC wall adapters. AC power is rectified and filtered by D1-4, C1, and C2 to create 2 C 3/99 the high voltage DC bus applied to the primary winding of T1. R4 and C3 clamp the primary leakage spike and also reduce EMI. At this power level, a simple RC network is sufficient for snubbing leakage spikes. Because of the relatively low switching frequency of TinySwitch (44 kHz), and its ON/OFF control method, the additional capacitive loading of the RC snubber network has a much smaller effect on efficiency than for conventional PWM switchers running at higher switching frequencies. Since TinySwitch runs in current limit mode at all times regardless of output load, the worst case leakage spike RD8 Component Listing Reference Value Part Number Manufacturer C1, C2 C3 C4 C5 C6 C7 D1-4 D5 L1 L2 R1 R2 R4 T1* U1 U2 VR1 4.7 µF, 400 V 68 pF, 1 kV 0.1 µF, 50 V 2.2 nF, 250 VAC Y1 330 µF, 16 V Low ESR 100 µF, 25 V 600 V, 1 A 60 V, 1A, Schottky 5.5 mH (min), 0.1 A Ferrite Bead, 3.5 X 11.4 mm 2.2 Ω, 1 W 4.7 kΩ, 1/4 W 1.5 kΩ, 1/2 W, 5% 475CKH400M DD680 RPE121Z5U104M50V 440LD22 ECA-1CFQ331L ECE-A1EGE101 1N4005 11DQ06 Illinois Capacitors Philips Murata Cera-Mite Panasonic Panasonic General Instrument International Rectifier 2743008112 BW2F2.2Ω5% 5043CX4K700J 5053CX1K500J TRD8 TNY254P LTV817 1N5237B Fair-Rite RCD Philips Philips Custom Power Integrations Liteon Motorola Optocoupler 8.2 V 5% Zener * For transformer sources, please visit the Power Integrations website at www.powerint.com. Table 2. Parts List for the RD8. and the appropriate values of R4 and C3 required for snubbing are easily determined. Traditional RCD or diode-Zener clamping can also be used at a small additional cost for higher efficiency. The secondary winding of T1 is rectified and filtered by D5, C6, L2, and C7 to create the 9 V output voltage. Zener diode VR1 and U2 sense the output voltage and provide feedback to TinySwitch U1. The output voltage is set by the combined voltage drops of Zener diode VR2 and the LED of U2. Other output voltages are also possible by adjusting the transformer turns ratio and the value of Zener diode VR1. A resistor can be placed across the LED of U2 to provide additional bias current (1-5 mA) to VR1. This improves regulation and voltage accuracy. The extra bias current slightly increases no load power consumption (15-75 mW). Capacitors C1, C2, L1, R2, and Y1-capacitor C5 provide EMI filtering for the power supply. At lower output power levels (or for supplies designed to operate at 115 VAC only), L1 can be replaced with a resistor, reducing system cost at the expense of slightly lower efficiency. Resistor R1 is a fusible resistor for protection against primary fault conditions. This is a low cost alternative to a standard fuse, accepted by safety agencies. The RD8 power supply is designed to run in discontinuous conduction mode, with the primary peak current set by the TNY254P internal current limit. In this mode of operation, the on-time for each switching cycle is set by the transformer primary inductance, TinySwitch current limit and the high voltage DC input bus. Output regulation is accomplished by skipping switching cycles in response to an ON/OFF feedback signal applied to the ENABLE pin. This differs significantly from traditional PWM schemes that control the duty factor of each switching cycle. Due to the ON/OFF nature of the TinySwitch control scheme, the feedback optocoupler operates in switching rather than in linear mode. Therefore the current transfer ratio is not a critical factor as long as the optocoupler provides enough current (50 µA) to activate the ENABLE pin of the TinySwitch. This allows a low cost ungraded optocoupler to be used. For 115 V applications, 200 V rated capacitors can be used for C1 and C2, and D5 can be replaced with a 40 V device (1N5819 or similar). If 200 V capacitors are used, then L1 can be replaced with a resistor. The circuit performance data shown in Figures 4-17 were measured with AC voltage applied to the RD8. Load Regulation (Figure 4) – The change in the DC output voltage for a given change in output current is referred to as load regulation. RD8 output voltage stays within ± 1% of nominal from 0% to 100% of rated load current. The TinySwitch regulation scheme enables this level of performance without the use of a preload. The slight rise in output voltage at no load is due to an increase in the voltage drop across VR1, caused by C 3/99 3 RD8 General Circuit Description (cont.) higher average Zener current. This effect can be corrected by adding a Zener bias resistor across the LED side of U2. This resistor also provides a small preload, further improving no load regulation. Line Regulation (Figure 5) - The change in the DC output voltage for a given change in the AC input voltage is called line regulation. The maximum change in output voltage versus line for the RD8 is within ± 0.5%. Efficiency (Line Dependent) – Efficiency is the ratio of the output power to the input power. The curves in Figures 6 and 7 show the efficiency as a function of input voltage. Note that the efficiency is relatively constant over the entire input voltage range. Efficiency (Load Dependent) – The curves in Figures 8 and 9 show how the efficiency changes with output power for 115 VAC and 230 VAC inputs. Due to the TinySwitch regulation scheme, the efficiency is relatively constant from 0-100% of output load. Power Supply Turn On Sequence –The waveforms shown in Figure 10 illustrate the relationship between the high-voltage DC bus and the 9 V output voltage. Since the TinySwitch internal power consumption is extremely small and is derived entirely from the DRAIN, the supply starts switching almost as soon as power is applied, as shown in Figure 10. The output achieves regulation approximately 8 ms after power is applied, with no overshoot. Power Supply Turn Off Sequence - Figure 11 shows the decay of the 9 V output when the AC input is removed. The 9 V decays monotonically to zero after AC power is removed, with no spurious pulses. Output Ripple - Line frequency ripple voltage is shown in Figure 12 for 115 VAC input and 3 W output. Switching frequency ripple voltage is shown in Figure 13 for the same test condition. In Figure 13, note the skipped pulses due to the TinySwitch ON/OFF control. Load Transient Response - The output transient response to a step load change from 0.26 to 0.33 A (75% to 100%) is shown in Figure 14. Note that the load transient is extremely small (< 20 mV), and recovers within 100 µs. The small step in the load response is due to the finite load regulation of the RD8. No Load Power Consumption - Figure 15 shows no load power consumption as a function of input voltage. The no load power consumption for the RD8 is only 10 to 20% of the standby power consumption of a typical linear power supply. 4 C 3/99 The RD8 is designed to meet worldwide safety and EMI (FCC B and VDE B) specifications. Measured conducted emissions are shown in Figure 16 for 115 VAC and Figure 17 for 230 VAC. In the RFI measurements performed on the RD8, peak measurements were applied to the quasi-peak limits specified by the test agencies. A peak measurement is more stringent than a quasi-peak or average measurement, since there is no averaging of the EMI signal form the supply under test. Peak measurements are also simpler and easier to perform using a standard spectrum analyzer. Figure 16 shows the results of a peak EMI scan at 115 VAC and full output load, compared to the FCC B quasi-peak limit. The RD8 passes the FCC B quasi-peak limits with margin using a peak EMI measurement. Applying quasi-peak measurement to the RD8 will result in EMI levels 3-4 dB lower than shown in Figure 16. This is true because the RD8 skips pulses to achieve regulation, resulting in substantially lower quasi-peak and average EMI levels than for a peak measurement. Most European EMI standards specify test limits for both quasi-peak and average measurement. The supply under test must pass both the average and quasi-peak limits to achieve certification. Figure 17 shows peak and average EMI scans performed at 230 VAC input and full load, compared to the VFG243 B quasi-peak limit and the VFG46 B average limit. The VFG243 and VFG46 specifications incorporate the same test limits as CISPR22, but also include frequencies below 150 kHz. The RD8 peak measurement passes the VFG 243 B quasi-peak limit with substantial margin, and almost passes the VFG46 B average limit. The average measurement passes the VFG46 B average limit with a minimum of 6 dB margin. In both the 115 V and 230 V measurements, there is almost no EMI at frequencies of 4 MHz and above. This is due in part to the relatively low operating frequency of TinySwitch (44 kHz nominal). The lack of high frequency emissions allows easy compliance with international radiated emissions limits. Transformer Specification The electrical specifications and construction details for transformer TRD8 are shown in Figures 18 and 19. Transformer TRD8 is supplied with the RD8 reference design board. Since no auxiliary bias winding is required to power TinySwitch, the transformer design is very simple, requiring only a primary and secondary winding. The TRD8 design utilizes an EE16 core and a triple insulated wire secondary winding. The use of triple insulated wire allows the transformer to be constructed using a smaller core and bobbin than a conventional magnet wire design due to the RD8 100 95 0 100 200 300 400 Load Current (mA) 105 VIN = 230 VAC 100 105 100 95 100 200 300 PO = 3 W 50 150 200 250 300 105 100 95 400 PO = 0.6 W 50 Load Current (mA) 100 150 200 250 300 Input Voltage (VAC) Figure 5. Line Regulation. PI-2260-091698 100 Po = 3 W 80 60 40 20 100 Po = 0.6 W Output Efficiency (%) Figure 4. Load Regulation. Output Efficiency (%) 100 Input Voltage (VAC) 95 0 PI-2258-091698 VIN = 115 VAC PI-2262-091698 Output Voltage (% of Nominal) 105 PI-2256-091698 If a conventional margin wound transformer is desired, the design of Figures 20-21 can be used. This design (TRD8-1) uses an EEL16 core and bobbin to accommodate the 6 mm total creepage distance required to meet international safety standards when using magnet wire rather than triple insulated wire. It has the same pinout and printed circuit foot print as TRD8. The margin wound transformer is approximately 50% taller than the triple insulated wire design due to the inclusion of creepage margins required to meet international safety standards. Output Voltage (% of Nominal) elimination of the margins required for safety spacing in a conventional design. 80 60 40 20 0 0 50 100 200 Input Voltage (VAC) Figure 6. Efficiency vs. Input Voltage, 3 W Output. 300 50 100 200 300 Input Voltage (VAC) Figure 7. Efficiency vs. Input Voltage, 0.6 W Output. C 3/99 5 RD8 60 40 20 0 80 60 40 20 0 0 0.5 1 1.5 2.5 2 3 0 Output Power (W) 1 1.5 2 2.5 3 PI-2268-101598 DC BUS VOLTAGE PI-2270-101598 Figure 9. Efficiency vs. Output Power, 230 VAC Input. 150 14 Output Voltage (V) 100 50 0 OUTPUT VOLTAGE 10 0.5 Output Power (W) Figure 8. Efficiency vs. Output Power, 115 VAC Input. 12 10 8 6 4 5 2 0 10 0 0 20 0 Time (ms) Figure 10. Turn On Delay, 115 VAC Input. 1 2 Time (s) Figure 11. Output Turn Off. Output Voltage (mV) 40 PI-2274-101598 PI-2272-101598 60 Output Voltage (mV) PI-2266-091798 80 VIN = 230 VAC Output Efficiency (%) VIN = 115 VAC Output Efficiency (%) 100 PI-2264-091798 100 20 0 -20 -40 100 50 0 -50 -100 -60 0 25 Time (ms) Figure 12. Line Frequency Ripple, 115 VAC Input, 3 W Output. 6 C 3/99 50 0 100 Time (µs) Figure 13. Switching Frequency Ripple, 115 VAC Input, 3 W Output. 200 20 PI-2282-101698 PI-2276-101598 80 0 -20 Power (mW) 300 200 60 40 20 PO = 0 W 100 0 0 0 1 50 2 Figure 14. Transient Load Response (75% to 100% of load). 200 250 300 Figure 15. No Load Power Consumption. PI-2284-101698 120 120 80 60 40 VFG243B (QP) VFG46B (AV) Peak Scan Average Scan 100 Amplitude (dBµV) 100 Amplitude (dBµV) 150 AC Input Voltage (V) Time (ms) 20 100 80 PI-2323-101698 Output Current (A) Output Voltage (mV) RD8 60 40 20 FCC 15 B (QP) Peak Scan 0 0 0.01 0.1 1 10 Frequency (MHz) Figure 16. EMI Characteristics at 115 VAC Input. 0.01 0.1 1 10 Frequency (MHz) Figure 17. EMI Characteristics at 230 VAC Input. C 3/99 7 RD8 TRIPLE INSULATED SECONDARY TRANSFORMER (TRD8) 3 9 174 T #34 AWG 4 14 T #26 AWG Triple-insulated 6 PIN 3 4 6 9 1 10 4 5 FUNCTION HIGH-VOLTAGE DC BUS TinySwitch DRAIN SECONDARY RETURN OUTPUT CORE# - PC40 EE16-Z (TDK) GAP FOR AL OF 112 nH/T2 BOBBIN# - YC-1607 (Ying Chin Co., Ltd.) ELECTRICAL SPECIFICATIONS Electrical Strength 60 Hz, 1 minute, from pins 1-4 to pins 5-10 3000 VAC Creepage Between pins 1-4 and pins 5-10 6.00 mm (min) Primary Inductance All windings open 3400 µH ±10% Resonant Frequency All windings open 420 kHz (min) Primary Leakage Inductance Pins 6 and 9 shorted 120 µH (max) NOTE: All inductance measurements should be made at 40 kHz PI-2226-082498 Figure 18. Electrical specification of transformer TRD8. 8 C 3/99 RD8 TRIPLE INSULATED SECONDARY TRANSFORMER CONSTRUCTION 9 6 4 SECONDARY PRIMARY 3 WINDING INSTRUCTIONS Primary Start at Pin 3. Wind 174 turns of 34 AWG heavy nyleze wire in four layers. Finish on Pin 4. Secondary Winding Start at Pin 6. Wind 14 turns of 26 AWG triple insulated wire from left to right. Finish on Pin 9. Final Assembly Assemble and secure core halves. Glue according to Power Integrations instructions (see Power Integrations website: www.powerint.com). * Triple insulated wire sources. P/N: T27A01TXXX-3 Rubudue Wire Company 5150 E. La Palma Avenue Suite 108 Anaheim Hills, CA 92807 (714) 693-5512 (714) 693-5515 FAX P/N: order by description Furukawa Electric America, Inc. 200 Westpark Drive Suite 190 Peachtree City, GA 30269 (770) 487-1234 (770) 487-9910 FAX P/N: order by description The Furukawa Electric Co., Ltd 6-1, Marunouchi 2-chome, Chiyoda-ku, Tokyo 100, Japan 81-3-3286-3226 81-3-3286-3747 FAX PI-2228-082498 Figure 19. Construction details of transformer TRD8. C 3/99 9 RD8 MARGIN WOUND TRANSFORMER 3 174 T #34 AWG 4 9 PIN 14 T #26 AWG 5 1 4 FUNCTION 3 4 6 9 6 10 HIGH-VOLTAGE DC BUS TinySwitch DRAIN RETURN OUTPUT CORE# - PC40 EE16/24/5-Z (TDK) GAP FOR AL OF 182 nH/T2 BOBBIN# - YC1605 (Ying Chin Co., Ltd.) ELECTRICAL SPECIFICATIONS Electrical Strength 60 Hz, 1 minute, from pins 1-4 to pins 5-10 3000 VAC Creepage Between pins 1-4 and pins 5-10 6.0 mm (min) Primary Inductance All windings open 3400 µH ±10% Resonant Frequency All windings open 420 kHz (min) Primary Leakage Inductance Pins 6 and 9 shorted 120 µH (max) NOTE: All inductance measurements should be made at 40 kHz PI-2222-082198 Figure 20. Electrical specification of transformer TRD8-1. 10 C 3/99 RD8 MARGIN WOUND TRANSFORMER CONSTRUCTION TAPE TAPE MARGINS (2 PLACES) 9 6 SECONDARY 4 PRIMARY TAPE 3 WINDING INSTRUCTIONS Primary Start at Pin 3. Wind 174 turns of 34 AWG heavy nyleze wire in four layers. Finish on Pin 4. Reinforced Insulation Apply 3 layers of tape (polyester film, 17.5 mm (0.689 in) wide and 0.056 mm (2.2 mil) thick) for reinforced insulation. Safety Margin Construct margins on each side of bobbin using 3 mm wide tape on flange side of bobbin and 6 mm wide tape on pin side of bobbin. Match height of secondary winding. Secondary Winding Start at Pin 6. Wind 14 turns of 26 AWG heavy nyleze wire from left to right in a single layer. Finish on Pin 9. Outer Insulation Apply 3 layers of 17.5 mm tape for outer insulation. Final Assembly Assemble and secure core halves. Glue according to Power Integrations instructions (see Power Integrations website: www.powerint.com). PI-2224-082498 Figure 21. Construction details of transformer TRD8-1. C 3/99 11 RD8 For the latest updates, visit our website: www.powerint.com Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does not assume any liability arising from the use of any device or circuit described herein, nor does it convey any license under its patent rights or the rights of others. PI Logo and TOPSwitch are registered trademarks of Power Integrations, Inc. ©Copyright 1999, Power Integrations, Inc. 477 N. 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