EVAL6565N

AN1439 Application note 30 W AC-DC adapter with the L6565 quasi-resonant PWM controller Introduction This application note describes the evaluation board of the Quasi-resonant (QR) PWM controller L6565 (order code: STEVAL-ISC001V1 - previous code EVAL6565N) and presents the results of its bench evaluation. The board implements a 30 W, single-output (15 V/2 A), wide-range mains input, QR converter that can be used as a reference design for an AC-DC adapter, where good performance is to be achieved at low cost. March 2008 Rev 7 1/17 www.st.com Contents AN1439 Contents 1 Design specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 Evaluation board functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2/17 AN1439 List of tables List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. STEVAL-ISC001V1 evaluation board: electrical specifications . . . . . . . . . . . . . . . . . . . . . . 5 STEVAL-ISC001V1 evaluation board: bill of material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 STEVAL-ISC001V1: transformer specification (part number 558179, supplied by Albe s.r.l.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Limits set by European code of conduct on efficiency of external power supplies . . . . . . . . 8 STEVAL-ISC001V1: typical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 STEVAL-ISC001V1: line/load regulation and efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 STEVAL-ISC001V1: light-load input power (at Pout = 0.5 W) . . . . . . . . . . . . . . . . . . . . . . . 10 STEVAL-ISC001V1: no-load input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 STEVAL-ISC001V1: maximum power capability (measured at 0.95·Vout) . . . . . . . . . . . . . 10 STEVAL-ISC001V1: typical wakeup time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 STEVAL-ISC001V1 modified as per optimization steps 1 to 3: no-load input power measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3/17 List of figures AN1439 List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. 4/17 STEVAL-ISC001V1 evaluation board: electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . 5 STEVAL-ISC001V1: PCB layout, silk + bottom layer (top view). . . . . . . . . . . . . . . . . . . . . . 7 STEVAL-ISC001V1: full load, Vin = 100 VDC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 STEVAL-ISC001V1: full load, Vin = 380 VDC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 STEVAL-ISC001V1: half load, Vin = 100 VDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 STEVAL-ISC001V1: half load, Vin = 380 VDC (note uneven skipping) . . . . . . . . . . . . . . . 11 STEVAL-ISC001V1: no load, Vin = 100 VDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 STEVAL-ISC001V1: no load, Vin = 380 VDC (burst mode) . . . . . . . . . . . . . . . . . . . . . . . . 12 STEVAL-ISC001V1: full-load output ripple at Vin = 110 Vac: high freq. . . . . . . . . . . . . . . . 12 STEVAL-ISC001V1: full-load output ripple at Vin = 110 Vac: line freq. . . . . . . . . . . . . . . . . 12 STEVAL-ISC001V1: behavior upon short-circuit on the output. Vin=220 Vac . . . . . . . . . . . 13 STEVAL-ISC001V1: behavior upon short-circuit on D7. Vin=220 Vac . . . . . . . . . . . . . . . . 13 STEVAL-ISC001V1: load transient (at Vin = 220 Vac: Iout = 0.5 to 2.5 A). . . . . . . . . . . . . . 13 High-voltage active startup circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Low-consumption feedback network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 AN1439 1 Design specification Design specification Table 1 summarizes the electrical specifications of the application, Table 2 provides the BOM and Table 3 lists the transformer's specifications. The electrical schematic is shown in Figure 1 and the PCB layout in Figure 2. Table 1. STEVAL-ISC001V1 evaluation board: electrical specifications Input voltage range (Vin) 88 to 264 Vac Mains frequency (fL) 50/60 Hz Maximum output power (Pout) 30 W – – – Output Vout= 15 V ± 3%; Iout = 0 to 2 A; Vripple≤1% Minimum switching frequency (at 100 VDC input voltage) 60 kHz Target efficiency (at Pout= 30 W, Vin= 88÷264 Vac) η> 80% < 0.75 W (1) Maximum no-load input power 1. Compliant with European Code of Conduct on Efficiency of External Power Supplies, phase 2, 01.01.2003. Figure 1. F1 2A fuse STEVAL-ISC001V1 evaluation board: electrical schematic NTC1 10R R1 100 Vin 88V to 264Vac 3 T1 B1 DF06G C5 100 F 400V C14 47nF 400V D1 1N4148 D2 1N4148 D4 1.5KE220A D3 STTH1L06 C15 100pF 1kV 8 10 Q1 STP5NK80ZFP R6 220 L6565 R7 10 1 6 C7b 100nF C12 330 F 25V R15 5.6K 4 D6 1N4148 4 2 15V 2A R11 1.5K 1 IC3 PC817X1 7 IC1 L2 10 H C6 2.2nF Y1 5 R8 47K 5 3 4 C7 47 F 25V R16 220K R3 1.5M C10,C11 680 F 25V 1 R5 4.7 D5 1N4148 R2 1.5M D7 8 STPS8H100FP R9 1.5 R10 1.5 3 1 R4 18K C8 1nF C9 2.2nF R13 10K R12 33K 2 3 IC2 TL431 C13 560nF R14 2K 2 D01IN1303B The electrical specification is typical of an AC-DC adapter for consumer equipment, usually developed as an external unit. As such, it falls within the scope of the European "Code of Conduct on Efficiency of External Power Supplies" and is required to be "efficient" under noload conditions as specified in Table 4. The design target is to fulfill the phase 2 requirements, so as to be up-to-date until the year 2005, when phase 3 sets even more stringent limits. Some hints to upgrade the design according to phase 3 is given in the section Evaluation board optimization for minimum no-load consumption on page 13. 5/17 Design specification Table 2. 6/17 AN1439 STEVAL-ISC001V1 evaluation board: bill of material Symbol Value Note R1 100 Ω 5% R2, R3 1.5 MΩ R4 18 kΩ R5 4.7 Ω R6 220 Ω R7 10 Ω R8 47 kΩ R9, R10 1.5 Ω R11 1.5 kΩ R12 33 kΩ R13 10 kΩ R14 2 kΩ R15 5.6 kΩ R16 220 kΩ C5 100 µF 1 kV, Rubycon, MXR series or equivalent C6 2.2 nF Y1 class C7 47 µF 25 V electrolytic C7b 100 nF Plastic film or ceramic C8, C9 2.2 nF Plastic film or ceramic C10, C11 680 µF 25 V Rubycon, ZL series or equivalent C12 330 µF 25 V Sanyo, CG series or equivalent C13 560 nF Plastic film or ceramic C14 47 nF 400 V, polyester C15 100 pF 1 kV, Y5P, Panasonic or equivalent L2 10 µH ELC08D100E, R=44 mΩ, Panasonic or equivalent T1 558179 B1 DF06G 1A / 600 V bridge, DIP4, GI or equivalent D1, D2, D5, D6 1N4148 0.3 A / 75 V, glass case, Vishay or equivalent D3 STTH1L06 1 A / 600 V Turboswitch, F126, ST D4 1.5KE220A 220 V Transil, CB429, ST D7 STPS8H100FP 8 A / 100 V Schottky, TO-220FPAC, ST IC1 L6565 QR PWM controller, DIP8, ST (1) IC2 TL431CZ Shunt regulator, TO92, ST IC3 PC817X1J000F Optocoupler, Sharp or equivalent Metallic film See spec in Table 3. Supplied by Albe s.r.l. (Tel. +39 363 61493) AN1439 Design specification Table 2. STEVAL-ISC001V1 evaluation board: bill of material (continued) Symbol Value Note Q1 STP5NK80ZFP 1.9 Ω/ 800 V, TO220FP, ST NTC1 SSN550 NTC 10 Ω, Vishay or equivalent F1 T2A250V 2 A, 250 V ELU PCB --- FR-4, Cu single layer 35 µm, 95.8 x 64.7 mm 1. If not otherwise specified, all resistors are 1%, ¼ W Q1 and D7 are both provided with a 40 °C/W heatsink SK95/25/SA from Fischer Elektronik. Table 3. STEVAL-ISC001V1: transformer specification (part number 558179, supplied by Albe s.r.l.) Core E25/13/7, N67 material or 3C85 or equivalent Bobbin Vertical mounting, 10 pins Air gap ≈ 1 mm for an inductance 1-3 of 740 µH Leakage inductance < 20 µH (at 60 kHz) pins 1-3 with 4,5,7,8,9,10 shorted Windings Spec & build Figure 2. Pin start/end Winding Wire Turns Notes 1/2 Pri1 AWG26 40 Innermost winding 7/9 Sec1 2xAWG23 8 Pins 7-8 will be shorted on the PCB 8/10 Sec2 2xAWG23 8 Pins 9-10 will be shorted on the PCB 2/3 Pri2 AWG26 40 Pin2 will be cut for safety 4/5 Aux AWG32 8 Evenly spaced STEVAL-ISC001V1: PCB layout, silk + bottom layer (top view) 7/17 Design specification Table 4. AN1439 Limits set by European code of conduct on efficiency of external power supplies No-load power consumption Rated input power 1.1 Phase 1 01.01.2001 Phase 2 01.01.2003 Phase 3 01.01.2005 ≥0.3 W and < 15 W 1.0 W 0.75 W 0.30 W ≥15 W and < 50 W 1.0 W 0.75 W 0.50 W Š50 W and < 75 W 1.0 W 0.75 W 0.75 W Evaluation board functionality The minimum switching frequency (60 kHz at Vin = 100 VDC) has been chosen trading off the transformer's size against frequency-related losses. The reflected voltage has been chosen equal to 150 V, then ZVS is achieved only when the converter operates from the 110 V mains. This value seems to provide a good compromise between capacitive and switching losses at 220 V mains. To provide room for the leakage inductance spike, an 800 V Power MOSFET (STP5NK80ZFP) is used. To get 150 V reflected voltage, the primary-to-secondary turn ratio is made 1:10, which originates relatively low reverse voltages at the secondary side and allows the use of a Schottky rectifier as the secondary diode (D7). An STPS8H100FP has been selected. Two design choices have been done to meet the noload consumption target. First, the converter is started up with a charge pump consisting of D1, D2, C14 and R1 instead of the usual dropping resistor. This circuit, usable thanks to the extremely low startup current of the L6565, provides a typical wakeup time going from 2.8 s at 88 Vac to 0.75 s at 264 Vac, while dissipating less than 50 mW at 264 Vac, i.e. saving about 200 mW as compared to a startup circuit made with a dropping resistor that gives the same wakeup time. Second, the leakage inductance spikes are handled by a Transil clamp (D4, with the addition of D3 to prevent direct conduction during Power MOSFET's ON-time), instead of an RCD clamp, thus saving about 200 mW more. R2+R3 and R4 compensate for the power capability change vs. the input voltage (Voltage Feedforward). Their ratio has been found simply by fixing the high side one (using a high resistance value to keep the losses low) and varying the low side resistance until the converter loses output voltage regulation with the same load at 88 and 264 Vac. A 1nF film capacitor bypasses any noise on pin #3 to ground. To stay within ± 3% tolerance, the output voltage regulation is done with secondary feedback, using a typical arrangement TL431+optocoupler. R12, C13 and C9 (on the primary side) compensate the voltage loop for stability. Typically, the crossover frequency is 5 kHz with 70° phase margin. A 100 pF low-loss capacitor (C15) has been added across the primary winding to optimize the Power MOSFET's losses at maximum load by a small snubbing effect on the drain voltage rate of rise. The delay between transformer' s demagnetization and the Power MOSFET's turn-on is adjusted by means of R8. The final value of 47 kΩ has been experimentally determined so as to achieve the optimum turn-on point (after the addition of C15). The converter is fully protected against short-circuit. Under this condition it operates at the frequency of the internal starter (2.5 kHz) and the reflected voltage on the auxiliary winding drops, hence the supply voltage of the L6565 cannot be maintained. This results in 8/17 AN1439 Design specification intermittent operation ("hiccup" mode) with low power throughput (< 1 W at 264 Vac). R10 prevents improper Power MOSFET's turn-on, due to signal bouncing on the pin, by pulling up the ZCD pin that would be completely floating otherwise. Additionally, thanks to the 2nd overcurrent level on the L6565's current sense pin, also a short-circuit directly across the secondary winding - or D7 failing short - causes an intermittent operation with an even lower level of power throughput. Board evaluation: getting started The AC voltage, generated by an AC source ranging from 88 Vac to 264 Vac, is applied to connector M1 (at the bottom left-hand corner). Should one want to use a high-voltage DC source, remember that the startup charge pump would not work and a dropping resistor would be needed to let the L6565 start. The 15 VDC output (connector M2) is located close to the bottom right-hand corner and will be connected to the load. If an electronic load is going to be used in CC mode, make sure that the voltage which the load starts sinking current at is > 1 V or use CR mode if this cannot be set, otherwise the board may not start up at maximum load. This happens because Vout needs to build up a little in order for the ZCD signal to be large enough to trigger QR operation (refer to 2.: "L6565 Quasi-Resonant Controller" (AN1326).) Before that, the converter runs at the frequency of the internal starter, with a much lower power capability that may be easily exceeded if the load starts sinking the maximum current as Vout is just above zero. In this case Vout gets clamped at a low value, the ZCD signal cannot reach the minimum amplitude required, QR operation cannot take place and the system cannot start up. Caution: Like in any offline circuit, extreme caution must be used when working with the application board because it contains dangerous and lethal potentials. The application must be tested with an isolation transformer connected between the AC mains and the input of the board to avoid any risk of electrical shock. Board evaluation: bench results and significant waveforms Table 5, 6, and 7 summarize the results of some bench evaluations. A number of waveforms under different load and line conditions are shown for the user's reference. Table 5. STEVAL-ISC001V1: typical performance Parameter Value Unit Regulated output voltage (at Vin= 220 Vac, Iout= 2 A) 14.924 V Minimum operating frequency (at Vin= 88 Vac, Iout= 2 A) 60 kHz Maximum operating frequency (at Vin= 264 Vac, Iout= 1.1 A) 214 kHz Line regulation (Vin = 88 to 264 Vac, Iout= 2 A) 1 mV Load regulation (Vin= 88 Vac, Iout= 0 to 2 A) 55 mV High-frequency output voltage ripple (at Vin= 88 Vac, Iout= 2 A) 10 mV Line-frequency output voltage ripple (at Vin= 88 Vac, fL = 60 Hz, Iout= 2 A)