october 2007 rev 4 1/8 AN1246 application note vipower: auxiliary bias power supply using viper20a-e introduction this application note describes a bias power supply to meet the needs of powering up power mosfets as well as providing standby power when the main unit is off. the viper20adip-e, a part of stmicroelectro nics proprietary vipower (vertical intelligent power), is a current mode pwm with a 700 v avalanche rugged power 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 provid e an output of 10 w power capability for wide range input, or 20 w for single input voltage range. www.st.com
contents AN1246 2/8 contents 1 key features of the vi per20adip-e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 general circuit descripti on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 connecting the demoboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 burst mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6 performance and cost consi deration . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
AN1246 key features of the viper20adip-e 3/8 1 key features of the viper20adip-e adjustable switching frequency up to 200 khz current mode control burst mode operation in standby mode, meets ?blue angel? standards undervoltage lock-out with hysteresis integrated start-up supply avalanche rugged overtemperature protection primary or secondary regulation general circuit description 2 general circuit description this demo board (see schematic in figure 1 ) is a 110 to 375 v dc input discontinuous flyback, working at 100 khz. the output can deliver 12 v at 0.5 a 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 which manages 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 optimi ze stability during tran sients. the demoboard can be tested with convection air. depending on the final application, air flow might be needed to keep the viper20adip-e under the thermal shutdown limit. figure 1. schematic c12 220pf 1kv cs6 .47u rs5 1.37k r6 150 r7 5.23k rs10 nu f1 0.5 a pico fuse 16t c3 120uf 16v c9 2.2n y cap 128t c7 680uf 16v j1 con 1 2 cs4 3.9nf ds2 stps1h100a rs4 1.6 d4 nu 14t r11 2.7k j2 con 1 2 r9 3.9 rs14 82k cs11 47n r8 1.2k cs5 33n c10 220pf 1kv ic2 tl431 a c r ds3 ll4148 rs2 4.99k c2 4.7uf 400v l2 10uh c8 330uf 16v ic1 viper20adip -e 2 3 8 7 1 6 4 5 vdd source drain drain osc drain comp drain d1 byt11-600 rs3 5.1k cramer coil csm 1608-027 t1 3 2 4 1 6 7 ic3 h11a817a 1 2 4 3
general circuit description AN1246 4/8 figure 2. pc board top legend bottom foil and surface mount components table 1. electrical specification from measured results parameter results input voltage range j1 110 to 375 v dc output j2 12 v from 0 to 0.5 a load regulation (0 to 0.5 a) from setpoint +/-25 mv or +/-0.2% line regulation (at max load) +/-1 mv efficiency 84% at 120 v dc and 79% at 375 v dc output ripple voltage 35 mv max input power at no load 0.65 w max transient response, 50% load step +/-60 mv typical table 2. component list quantity reference description value 1 c2 f4.7 f 400 v 1 c3 120 f 16 v (low esr) 1 cs4 3.9 nf 50 v 1 cs5 33 nf 50 v 1 cs6 47 f 25 v 1 c7 680 f 16 v (low esr) 1 c8 330 f 16 v (low esr) 1 c9 y1 rated safety cap 2.2 nf 1 c10 220 pf 1 kv 1 cs11 47 f 50 v 1 c12 220 pf 1 kv 1 d1 byt11-600 (1) 600 v 1 a ultrafast
AN1246 general circuit description 5/8 figure 3. cross section of the transformer 1 ds2 stps1h100a (1) 100 v 1 a schottky 1 ds3 ll4148 1 f1 fuse 0.5 a pico 1 ic1 viper20adip-e (1) 1 ic2 tl431 (1) 1 ic3 h11a817a (optocoupler) 1 j1 connector terminal 1 j2 connector terminal 1 l2 coilcraft pch-27-103 10 h 1 rs2 4.99 k ? 1% 1/8 w 1 rs3 5.1 k ? 1/8 w 1 rs4 1.6 ? 1/8 w 1 rs5 1.37 ? 1% 1/8 w 1 r6 150 ? 1/4 w 1 r7 5.23 k ? 1% 1/4 w 1 r8 1.2 k ? 1/4 w 1 r9 3.9 ? 1/4 w 1 r11 2.7 k ? 1/4 w 1 rs14 82 k ? 1/4 w 1 t1 cramer coil csm 1608-027 1. parts available from stmicroelectronics . ?s? in legend denotes a surface mount part. table 3. transformer specification parameter value primary inductance 1.65 mh core c40 ee16 table 2. component list (continued) quantity reference description value
connecting the demo board AN1246 6/8 3 connecting the demo board 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 v dc . connect an electronic load or resistive load to j2. 4 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 viper20adip-e pin 3 on the printed circuit lay out. when signal paths share the same trace as a power path, instabilit ies may result. the compensation components, cs6, rs3, and cs4 are on a separate trace connected directly to the source of the device. 5 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 waveform ( figure 4 ). v in is 375 v dc i out is at no load. as can be seen, there is one pulse out of te n pulses to reduce power consumption. the output ripple is negligible.
AN1246 revision history 7/8 figure 4. burst mode waveform 6 revision history table 4. document revision history date revision changes 04-jan-2004 3 minor text changes 18-oct-2007 4 ? document reformatted no content change ? viper20a replaced by viper20a-e ? viper20adip replaced by viper20adip-e
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