(R) AN1246 - APPLICATION NOTE VIPower: AUXILIARY BIAS POWER SUPPLY USING VIPer20A J.S. Lo Giudice INTRODUCTION Most power supplies and associated logic circuitry need a means of powering up the switching regulator, MOSFETs. This application note describes a bias power supply to meet these needs and also provide standby power when the main unit is off. The VIPer20A, a part of STMicroelectronics proprietary VIPower (Vertical Intelligent Power), is a current mode PWM with a 700 volt avalanche rugged MOSFET. It uses a fabrication process which allows the integration of analog control circuits with a vertical power device on the same chip. It can provide an output with 10W power capability for wide range input, or 20W for single input voltage range. KEY FEATURES OF THE VIPer20A n Adjustable switching Frequency Up to 200KHz n Current mode Control n Burst Mode Operation in Stand-by Mode, Meets "Blue Angel" standards n Undervoltage Lock-out with Hysteresis n Integrated Start-up Supply n Avalanche Rugged n Overtemperature Protection n Primary or secondary Regulation GENERAL CIRCUIT DESCRIPTION This demoboard (see schematic in Fig. 1) is a 110 to 375 Vdc input discontinuous Flyback, working at 100 kHz. The output can deliver 12 volts at 0.5 amps continuous. This circuit can be powered from the: main bulk capacitors of an off-line power supply, power factor correction output stage, or the AC line with the addition of a low current bridge rectifier. It benefits from the EMI filter present in a typical power supply. The output uses a Schottky diode for better efficiency. C7 is a low ESR capacitor to manage the ripple current. IC2 provides the reference and the feedback to tightly regulate the output. CS5, CS6, and RS3 form the feedback loop compensation to optimize stability during transients. The demoboard can be tested with convection air. Depending on the final application, air flow might be needed to keep the VIPer20A under the thermal shutdown limit. February 2000 1/6 1 AN1246 - APPLICATION NOTE Figure 1: Schematic J1 R9 F1 2 1 3.9 0.5 A Pico Fuse D1 BYT11-600 CON T1 Cramer Coil CSM 1608-027 DS2 L2 C12 220pF 1KV 4 1 2 STPS1H100A 128T C7 C8 330uF 16V 16T 680uF 16V 3 2 RS4 1.6 DS3 LL4148 14T 7 1 C2 4.7uF 400V c9 2.2n Y cap C3 120uF 16V RS2 4.99K IC1 6 5 drain osc drain vdd drain source drain comp 1 2 R6 3 150 R8 1.2k 4 4 VIPer20ADIP CS5 CS6 IC3 33n .47u H11A817A 3 CS4 3.9nF D4 NU R7 5.23k 1 7 C 2 8 RS10 nu RS3 A 5.1k IC2 TL431 R CS11 47n RS5 1.37k ELECTRICAL SPECIFICATION FROM MEASURED RESULTS PARAMETER Input voltage range J1 Output J2 Load regulation (0 to 0.5A) from setpoint Line regulation (at max load) Efficiency Output ripple voltage Input power at no load Transient response, 50% load step 2/6 J2 10uH C10 220pF 1KV RS14 82K 6 RESULTS 110 to 375 VDC 12V from 0 to 0.5A +/- 25mV or +/- 0.2% +/- 1mV 84% at 120VDC and 79% at 375 VDC 35 mV MAX 0.65W MAX +/-60 mV typical R11 2.7k CON AN1246 - APPLICATION NOTE PC BOARD TOP LEGEND BOTTOM FOIL AND SURFACE MOUNT COMPONENTS COMPONENT LIST QUANTITY 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 REFERENCE C2 C3 CS4 CS5 CS6 C7 C8 C9 C10 CS11 C12 D1 DS2 DS3 F1 IC1 IC2 IC3 J1 J2 L2 RS2 RS3 RS4 RS5 R6 R7 R8 R9 R11 RS14 T1 DESCRIPTION Y1 Rated safety cap *BYT11-600 *STPS1H100A LL4148 fuse *VIPer20ADIP *TL431 H11A817A (optocoupler) Connector terminal Connector terminal Coilcraft PCH-27-103 VALUE F4.7F 400V 120F 16V (low ESR) 3.9nF 50V 33nF 50V 47F 25V 680F 16V (low ESR) 330F 16V (low ESR) 2.2nF 220pF 1KV 47F 50V 220pF 1KV 600V 1A Ultrafast 100V 1A Schottky 0.5 A pico 10H 4.99K 1% 1/8W 5.1K 1/8W 1.6 1/8W 1.37 1% 1/8W 150 1/4W 5.23K 1% 1/4W 1.2K 1/4W 3.9 1/4W 2.7K 1/4W 82K 1/4W Cramer Coil CSM 1608-027 * Parts available from STMicroelectronics. "S" in legend denotes a surface mount part. 3/6 AN1246 - APPLICATION NOTE TRANSFORMER SPECIFICATION Primary inductance Core 1.65mH C40 EE16 CONNECTING THE DEMOBOARD This demo board has two connectors. Connect a DC voltage source capable of delivering up to 400 volts DC to connector J1. Be sure to connect the positive source to the + terminal of J1 and the negative to the - terminal before turning on the input power. The minimum voltage to operate this demo board is 110 volt DC. Connect an electronic load or resistive load to J2. LAYOUT CONSIDERATIONS Some simple rules to improve performance and minimize noise should be followed: 1. Minimize power loops. The switched power current paths inner loop area must be as small as possible. This can be accomplished by careful layout of the printed circuit board and the use of surface mount components. This avoids radiated and conducted EMI noise, and improves the efficiency by eliminating parasitic inductance, thus reducing or eliminating the need for snubbers and EMI filtering. 2 Use separate tracks for low level signal and power traces carrying fast switching pulses. This can be seen on the VIPer20A pin 3 on the printed circuit lay out. When signal paths are sharing the same trace as a power path, instabilities may result. The compensation components, CS6, RS3, and CS4 are on a separate trace connected directly to the source of the device. BURST MODE When the output current is too low, the burst mode operation takes over automatically. This results in missing cycles as shown on the following scope wave form (Figure 2). Vin is 375 Vdc Iout is at no load. As can be seen, there is one pulse out of ten pulses to reduce power consumption. The output ripple is negligible. PERFORMANCE AND COST CONSIDERATION This demo board has been optimized for performance. Cost trade off can be accomplished by configuring the VIPer for primary regulation. The output regulation will degrade to +/- 5% but the cost of the optocoupler, the TL431 and 5 other passive components can eliminated. If more output ripple voltage can be tolerated, than L2 and C8 can be eliminated. 4/6 AN1246 - APPLICATION NOTE Figure 2: Burst mode Waveform 5/6 1 AN1246 - APPLICATION NOTE Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may results from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics 2000 STMicroelectronics - Printed in ITALY- All Rights Reserved. STMicroelectronics GROUP OF COMPANIES Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - U.S.A. http://www.st.com 6/6 1