DI-148 Design Idea PeakSwitch

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Nội dung Text: DI-148 Design Idea PeakSwitch

DI-148 Design Idea ® PeakSwitch Multiple Output Flyback Power Supply for Audio Amplifier Using Magnetic Amplifiers to Achieve Better Cross Regulation Application Device Power Output Input Voltage Output Voltage Topology Audio PKS607YN 75 W, 126 W Peak 195 - 265 VAC ±26 V, ±15 V, 5 V Flyback Design Highlights Operation • Effectively replaces linear transformer-based power supplies in The universal input power supply shown in Figure 1 has multiple home audio applications outputs, ±26 VDC, ±15 VDC, and +5 VDC. The ±26 V outputs • Dramatically reduces weight, allowing chassis cost reduction can each deliver a minimum output current of 2.42 A peak (ther- • Proprietary magnetic ampliﬁer (mag amp) approach enables mally limited) and 1.45 A continuous. Additionally, the voltage tight cross regulation of two main outputs in ﬂyback topology regulation and, importantly, transient response is excellent over the • Low component count, compact and light weight. entire load range (no-load to full load). • Energy efﬁciency • >82% efﬁciency at full load The controller in U1 skips switching cycles to regulate the output • 25 μA ﬂows into the EN/UV pin. • Accurate, auto-recovering, hysteretic thermal shutdown func- tion maintains safe PCB temperatures under all conditions • Latching shutdown protects against output short circuits and open feedback loops C9 2.2 nF R16 C23 15 V, 150 mA 68 7 250 VAC 1/2 W 330 pF C27 IN OUT IN OUT 47 MF IN OUT 5 V, 150 mA 1 U5 10 V U8 12 U6 LM7915 UA7815 LM78L05 -15 V, 150 mA D7-8,D16-17 C6 VR1 D6 GND 1N4007 P6KE91A GND GND C7 470 pF UF4002 R52 C13 C20 4700pF 1 kV 2,3 68 k7 L2 330 MF 680 nF C28 1 kV VR2 10 100 MF RTN 1/2 W MP1305 50 V 50 V R6 P6KE91A 25 V C45 1507 11 -26 V, 1.45 A 100 MF 1/2 W VR3 D9 C14 C16 4 BYV32- 400 V P6KE91A C49 330 MF 680 nF N.C. 200 50 V 50 V 470 pF R7 8,9 100 V 2.2 7 D2 UF4005 C50 C19 C26 RTN R53 470 pF 100 MF 100 MF L3 D13 25 V 68 k7 100 V BAV20 25 V MP1305 7 1/2 W D5 C10 C11 C15 26 V, 1.45 A 5 D3 1N4148 R47 2.7 k7 BYV32- 330 MF 330 MF 680 nF RT1 D20 200 50 V 50 V 50 V C47 R49 SB160 VR4 1 nF 1N5253B O 6 50 V 10 7 t 1/2 W Q2 25V R4 T1 MPSA42 L1 EER28 10 mH 2 M7 R48 C34 PeakSwitch 5.1 k7 100 nF R21 U1 1/8 W 50 V 130 7 R5 C5 C1 PKS607YN 2 M7 R3 47 uF 330 nF 4.7 k7 35 V 275 VAC D D21 EN/UV C8 R24 1N4148 2.2 nF 510 7 BP 250 VAC S GND U2B R43 R1 R2 U2A 1.3 M7 1.3 M7 PC817D 1 k7 PC817D R51 R23 F1 Q3 100 7 2N3904 510 7 3.15 A C17 C18 1/2 W C4 220 pF 220 pF R50 330 nF R46 D11 250 VAC 250 VAC 10 7 5.1 k7 1N4148 1/8 W D19 D12 1N4148 D10 C48 D22 BAV20 33 pF 1N4148 1N4148 Q1 VR5 1 kV 2N5401 1N5254B R26 27 V L PE N 2 k7 195 - 265 U7A 3 C35 VAC LM358P 220 nF 2 50 V R45 D18 2.7 k7 SB160 R44 100 k7 R30 PI-4884-021108 R32 1 k7 49.9 k7 1% C39 R31 R27 C37 C46 49.9 k7 1 k7 1 nF 10 nF 47 MF 50 V 1% 50 V 10 V Figure 1. Schematic of a 75 W Continuous and 126 W Peak Audio Ampliﬁer Power Supply. www.powerint.com February 2008
The primary feedback circuit is closed across the ±26 V (52 V) • The core size and the winding wire diameter sizes (see Table 1) outputs via VR4, U2A and VR5. This ensures that the sum of were chosen based on the average of the peak and the voltages across the ±26 V outputs is regulated. For improved continuous output power. cross-regulation, two separate magnetic ampliﬁers (mag amps) • An RC snubber (R51and C48) was added between drain and are used on the ±26 V outputs. A mag amp is a saturable reactor source of U1 to reduce radiated EMI. or inductor that uses a core material that has a rectangular B-H curve. Adjusting the current (magnetic ﬂux) in the mag amp 80 PI-4885-110707 adjusts the period that it blocks current ﬂow. 70 Here two magnetic ampliﬁers (L2 and L3) are used for improved QP 60 cross regulation. This is especially relevant for audio designs as AV power is drawn from the supply at audio frequencies. The highest 50 output power component occurs at lower frequency where current 40 is alternately drawn from each output but not simultaneously. dBµV 30 By adjusting the current in L2 and L3, the circuitry formed by U7A, 20 Q1 and Q2 determines the proportion of the energy stored in the transformer that is delivered to the +26 V and -26 V outputs 10 during the off time of the PeakSwitch internal MOSFET. At the 0 extreme, with one output fully loaded and the other at no-load, almost all the energy is delivered to the output under full load. -10 Importantly, both outputs cannot be simultaneously blocked, -20 which would cause excessive clamp dissipation. Even with very 0.15 1.0 10.0 100.0 large load transients 25%-100% that are common in audio MHz supplies, the output regulation is maintained within ±5% on both Figure 2. Conducted EMI at 230 VAC With Output Grounded (Worst Case). outputs. Common mode choke, L1, and the two Y-capacitors, C8 and C9, Transformer Parameters form the common mode EMI ﬁlter. Common mode choke L1 also works in conjunction with X-capacitor C1 to provide differential EER28 NC-2H or equivalent, Core Material mode EMI ﬁltering. gapped for ALG of 139 nH/t² Bobbin EER28, 12 pin, Vertical Key Design Points • The high crest factor of the music source allows physically Add 3 mm margins on both sides of bobbin Primary: 16T × 2, AWG30, tape smaller heatsinks. Shield: 1T × 1, foil 2 mils thick, 3 layers tape • The auxiliary ±15 VDC and +5 VDC outputs are obtained from +26 V: 8T × 2, AWG23, 1 layer tape a linear regulator. To limit the power dissipation in the (5 V and Winding Details -26 V: 8T × 2, AWG23, 1 layer tape 15 V) linear regulators, a second 18 V output was added to 18 V: 6T × 2, AWG28, tape transformer T1. Bias: 5T × 2, AWG30, tape • As the value of X capacitor C1 is above 0.1 μF, safety agency Primary: 17 T × 2, AWG30, 2 layers tape requirements specify that it R1 and R2 should be used to Primary (4–2), Shield (NC–1), +26 V (7–8), -26 V Winding Order discharge C1. Resistors R1 and R2 are chosen such that (9-11), 18 V (12-10), Bias (5-6), Primary (2-1) (R1 + R2) × C1 ≤ 1 s. Primary Inductance 151 μH, ±20% • To reduce grouping of switched cycles, a high gain optocoupler, U2, was used to drive small signal transistor Q3, which pulls Primary Resonant 2 MHz (minimum) Frequency current out of the EN/UV pin. Capacitor C34 adds high frequency gain to the feedback signal. Leakage Inductance 5 μH (maximum) • In a three wire system, placing Y capacitors (C17, C18) between line/neutral and earth helps reduce common mode EMI. Table 1. Transformer Parameters. (NC = No Connection, TIW = Triple Insulated Wire) Power Integrations Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power 5245 Hellyer Avenue Integrations does not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS San Jose, CA 95138, USA. MAKES NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED Main: +1 408-414-9200 WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. Customer Service The products and applications illustrated herein (transformer construction and circuits external to the products) may be covered by Phone: +1-408-414-9665 one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. Fax: +1-408-414-9765 A complete list of Power Integrations' patents may be found at www.powerint.com. Power Integrations grants Email: usasales@powerint.com its customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm. The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch, PeakSwitch, EcoSmart, Clampless, E-Shield, Filterfuse, StackFET, On the Web PI Expert and PI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies. www.powerint.com ©2007, Power Integrations, Inc. A 02/08 DI-148