DN05058/D Design Note – DN05058/D NCP107X, 12 Vout, Off-line Buck Regulator Device Application Input Voltage Output Power Topology I/O Isolation NCP1071 NCP1075 NCP1077 Smart Meters Electric Meters, White Goods 85 to 265 Vac Up to 6 W at 12 Vout Off-Line 100 kHz Buck Non-isolated Output Specification Output Voltage Output Ripple Typical Current Max Current Min Current 5 to 36 Vdc depending on selected Z1 zener value Less than 1% 100 to 350 mA 150 mA with NCP1071, 400 mA with NCP1077 (see matrix below) zero PFC (Yes/No) Efficiency Inrush Limiting / Fuse Operating Temp. Range Cooling Method / Supply Orientation Signal Level Control No, Pout < 25 watts See plots below External fuse required 0 to +50°C (dependent on U1 heatsinking) Convection None Circuit Description This design note describes a very simple, low power, constant voltage output buck power converter intended for powering electronics for white goods, electrical meters, and industrial equipment where isolation from the AC mains is not required. The switching element in the converter is ON Semiconductor’s NCP107x series of monolithic switchers. In this reference design, the NCP1071 is utilized with a 100 kHz switching frequency and a maximum output current of 250 mA. This buck circuit design utilizes a simple charge pump or “bootstrap” type of voltage sensing and regulation scheme composed of D4, C5, Z1, Q1 and the associated passive components. This simple sensing technique eliminates the use of an optocoupler in the feedback loop. Z1 sets the approximate output voltage and Q1 acts as a simple error amplifier. Although the regulation is inferior to that of a conventional TL431 and optocoupler feedback circuit, it is typically adequate for most applications with a regulation of +/- 5% over loads from 100% December, 2013, Rev. 0 down to about 1% max rated load. Below 1% the output will rise to the value of the overvoltage clamping zener Z2 across the output. For a 12 volt output, a typical value for this zener will be 15 volts and at no load, the output will be clamped at this level. The sensed voltage produced on C5 is also used to power the NCP1071 controller through D2 and limiting resistor R1 once the converter has started. This auxiliary Vcc to run the chip improves the overall efficiency of the circuit and prevents the controller from running in DSS mode under normal load conditions. Because of the low power output, a simple halfwave input rectifier/filter circuit is used comprised of D1 and C2. C1 and L1 form a conducted EMI filter that easily meets CE and UL level B requirements. C2 can be reduced to ½ the specified capacitance if a full-wave bridge rectifier circuit is used on the input. The 1.5 mH buck output inductor is available in several surface mount configurations from multiple vendors. www.onsemi.com 1 DN05058/D Schematic U1 NCP107x-100 L1, 1 mH 0.6 A D1 85 - 270Vac + 4 2 MRA4007 AC input L2 1.5 mH 1 3 C1 100nF "x" C4 D3 C2 10 uF, 400Vdc R1 2K Q1 C8 + 22uF 25V R4 C7 100 R5 2K 470uF 16V 0.1uF 50V Z2 C6 R3 0.1 470 R2 4.7 ohms Z1 MMSZ 5242B (12V) Output 12V, 250mA _ MMSD4148A MMBTA06 10nF C3 MURA 160 D2 1N5929B (15V) D4 MURA160 + C5 22uF 25V Notes: 1. Vout set by Z1 (Vout = Vz + 0.5V approx - adjust with R5). 2. L1 is Wurth 744732102. 3. Z2 is optional output OVP zener (15V). 4. R1 sets Vcc max current to avoid OVP trip. 5. L2 is Wurth 7687709152 (1.5 mH, 500 mA) 6. Crossed schematic lines are not connected. Off-Line Buck Converter Using NCP1070 With Charge Pump Voltage Sensing (R4) Output Regulation December, 2013, Rev. 0 www.onsemi.com 2 DN05058/D Typical Efficiency vs Load at 120 Vac Input for NCP107x Series Output Ripple – 250 mA Load, 120 Vac Input December, 2013, Rev. 0 www.onsemi.com 3 DN05058/D Conducted EMI Profile (12Vout @ 250 mA) dBuV NCP1072 12V 3 Watt Buck 80 70 60 EN 55022; Class B Conducted, Quasi-Peak 50 EN 55022; Class B Conducted, Average 40 30 L Average 20 10 0 -10 -20 1 10 12/11/2013 10:35:44 AM (Start = 0.15, Stop = 30.00) MHz NCP107x Buck Converter Maximum Output Current Matrix Part NCP1070 NCP1071 NCP1072 NCP1075 NCP1076 NCP1077 Continuous Limit 100 mA 150 mA 150 mA 250 mA 300 mA 400 mA Peak Transient Limit 1500 mA 200 mA 200 mA 300 mA 350 mA 500 mA References: ON Semiconductor Application Notes: AND8318, AND8328 ON Semiconductor Design Notes: DN05014, DN05023, DN5053, DN06011, DN06052 ON Semiconductor NCP1070, NCP1075 and NCP1077 monolithic switcher data sheets. 1 © 2013 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 Frank Cathell, e-mail: [email protected] December, 2013, Rev. 0 www.onsemi.com 4 DN05058/D BOM Designator Qty Description D3, D4 D1 D2 Z1 Z2 U1 Q1 2 1 1 1 1 1 1 Ultra-fast rectifier Diode - 60 Hz, Signal diode Zener diode Zener diode Controller - NCP1070/1072 NPN transistor C1 C7 C4, C6 C2 C5, C8 C3 1 1 2 1 2 1 "X" cap, box type Ceramic cap, monolythic Ceramic cap, monolythic Electrolytic cap Electrolytic cap Electrolytic cap R2 R3 R4 R1, R5 1 1 1 2 Resistor, 1/8W SMD Resistor, 1/8W SMD Resistor, 1/8W SMD Resistor, 1/8W SMD L1 L2 1 Inductor (EMI choke) 1 Output Inductor December, 2013, Rev. 0 Value Tolerance 1A, 600V 1A, 800V 100mA, 100V 12V 15V/5W 100 kHz 60V, 500 mA Footprint Manufacturer Manufacturer Part Number SMA SMA SOD-123 SOD-123 Axial lead SOT223 SOT23 ON Semi ON Semi ON Semi ON Semi ON Semi ON Semi ON Semi MURA160 MRA4007 MMSD4148A MMSZ5242B 1N5352B or 1N5929B NCP1070-100 MMBTA06T1G/MMBT2222A 100nF, X2 10 nF, 50V 100nF, 50V 10uF, 400 or 450V 22uF, 50Vdc 470uF, 25V 10% 10% 10% 10% 10% LS = 10 mm 805 805 LS=5mm, 12 x 15.5mm LS=2.5mm, D=5mm 7.5x15mm, LS=3.5mm Rifa, Wima AVX, Murata AVX, Murata UCC Panasonic - ECG UCC, Panasonic TBD TBD TBD TBD TBD TBD 4.7 ohms 470 ohms 100 ohms 2K 5% 5% 5% 5% SMD 805 SMD 805 SMD 805 SMD 805 AVX, Vishay, Dale AVX, Vishay, Dale AVX, Vishay, Dale AVX, Vishay, Dale TBD TBD TBD TBD LS=5mm, Dia=7.5mm 12mm x 12mm SMD Wurth Magnetics Wurth 7447728215 7687709152 820 uH or 1 mH 1.5 mH, 500mA www.onsemi.com 5