DN06028/D Design Note – DN06028/D 7 W, Non-Isolated Buck AC-DC Converter Device NCP1055 Application Input Voltage 1 Output AC to DC converter 108-132 Vac Output Power Topology I/O Isolation 7 Watts Non-Isolated Buck Converter No Other Specifications Output 91 V 3V 75 mA 100 mA 8 mA Output Voltage Ripple Nominal Current Max Current Min Current PFC (Yes/No) No Inrush Limiting / Fuse Cooling Method/Supply Orientation None Convection Circuit Description This design note explains the changes required to modify the NCP1052 Buck Demo Board’s (AND8098/D) output from 12V/100mA into 91V/75mA. Please read the original NCP1052 evaluation board manual for reference 1 . Design Considerations NCP105X and Inductor The first step in the design process is determining which version of the NCP105x to use. Refer to the “NCP105x Discontinuous Mode Flyback Design Worksheet” 2 . The desired input voltages of this particular board range from 108 to 132 Vac (about 150 Vdc to 190 Vdc). The inductor is chosen to be around 390 μH, a slightly reduced value compared to the original NCP1052 circuit. The result from table 1 of the Worksheet indicates that the NCP1055 at 136 kHz can be used for the desired output power of 7 W. A different version NCP105X may be suggested by the Worksheet by simply changing the inductor value. The NCP1055 136 kHz version is used in this design. Zener Diodes The output voltage of the converter is set by the breakdown voltage of Z1. The breakdown voltage of the diode is calculated using the equation below: VZ 1 = Vout − 5V Capacitors Since the output voltage is increased to 91V, the output capacitor (C5) must be changed. An electrolytic capacitor is used as they are more readily available at this voltage level. The value of C5 is reduced to reduce cost. The value of the bulk input capacitor (C3) is increased from 10 μF to 33 μF to reduce the input voltage ripple to 3 V. C3 and C5 can be increased to reduce the output voltage ripple, or they may be reduced to reduce cost. Capacitor C2 is increased to increase the startup time. Finally, a filtering capacitor (C4) is added between the feedback pin and source pin to reduce noise into the feedback pin; this is a very important addition to the board. Unchanged Components Diodes D1, D2, D3, D4 and Capacitor C1 remain the same as the original NCP1052 board. 1 Available at http://www.onsemi.com/pub/Collateral/NCP1052EVB_MANUAL.PDF. 2 Available at http://www.onsemi.com/pub/Collateral/NCP105X_WORKSHEET.XLS June 2007, Rev. 0 This equation comes from application note AND8098/D. A 91 V output is achieved using an 86 V Zener. The breakdown of zener diodes can be added in series to obtain the desired breakdown voltage. In this design two 43 V Zeners in series are used for Z1. Zener diode Z1 is used in the original NCP1052 board to clamp the voltage down at light or no load. However, the higher voltage of this design requires a higher power dummy load (R2) to maintain the output in regulation when no load is present. It may be possible to use a lower frequency version of the NCP1055 and reduce the power rating of R2. www.onsemi.com 1 DN06028/D Key Features y Low-cost, simple design y Relatively few changes for output voltage change y Self-powered from high input voltage y Frequency jittering for low electromagnetic interference(EMI) y Thermal and short circuit fault protection Schematic Figure 1: Circuit Schematic Bill of Materials Designator Quantity Description Value Tolerance Manufacturer Manufacturer Part Number U1 D1, D4 D2 D3 Z1a, Z1b R1 R2 C1 C2 C3 C4 C5 L1 1 2 1 1 2 1 1 1 1 1 1 1 1 Switching Regulator Ultrafast Diode Switching Diode General Diode Zener Diode Chip Resistor Axial Resistor Ceramic Capacitor Tantalum Capacitor Electrolytic Capacitor Ceramic Capacitor Electrolytic Capacitor Inductor 680 mA / 136 kHz 1 A / 600 V 200 mA / 100 V 1 A / 600 V 43 V 2 kΩ / 250 mW 12 kΩ / 1 W 0.22 µF / 50 V 10 µF / 25 V 33 µF / 450 V 1000 pF / 50 V 10 µF / 250 V 390 µH / 450 mA N/A N/A N/A N/A 5% 5% 10% 10% 10% 20% 10% 20% 20% ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor Vishay Ohmite Vishay Vishay Panasonic Vishay Panasonic Coilcraft NCP1055ST136G MURS160T3 MMSD914T1 MRA4006T1 MMSZ5260BT1G CRCW12062K00JNEA OX123KE VJ1206Y224KXXA 595D106X9025B2T ECA-2WM330 VJ1206Y102KXXA ECA-2EM100 RFB0807-391L June 2007, Rev. 0 www.onsemi.com 2 DN06028/D 3 Output Waveforms* Figure 2: 89V Output at Full Load (Left: Vin=108Vac, Right: Vin=132Vac) Figure 3: 89V Output 3V Ripple (Left: Vin=108Vac, Right: Vin=132Vac) Figure 4: 89V Output at Startup (Left: Vin=108Vac, Right: Vin=132Vac) *Note: output waveforms in Figures 2 through 4 were taken using an 89 V version of the board. The only difference being the breakdown voltage of the Zener diodes. 3 © 2007 ON Semiconductor. Disclaimer: ON Semiconductor is providing this design note “AS IS” and does not assume any liability arising from its use; nor does ON Semiconductor convey any license to its or any third party’s intellectual property rights. This document is provided only to assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its products at any time, without notice. Design note created by David Berdy, e-mail: [email protected] June 2007, Rev. 0 www.onsemi.com 3