? AN1094/1198 1/7 1 1 introduction the present board prototype is a wide-range input off-line 50w single switch flyback, working at 100 khz. it is based on a new off-line smart switcher : the viper100. figure 1: standard demoboard - order code: viperkitbd the viper100 is a current mode pwm with a 620v / 2.5 w power switch, able to withstand an avalanche current during normal operation. the start up of the circuit is done with an internal high voltage current source, which is switched off during steady state. it also includes a regulation function designed to minimize the pin count, while maintaining design flexibility. figure 2 presents the internal block diagram of this monolithic device. such a device can be easily used in any off-line flyback smps, with a 100 w power capability for a single input voltage range, or 50 w with a wide input range. this stand-alone off-line smart switcher concept provides a cost effective solution for smps of many applications like vcr, tv sets, satellite receivers or decoders. the benefits for the customer are a simpler design phase and a reduced overall components count due to the optimization of the product configuration. application note off-line smps using viper100
2/7 application note 1.1 viper100 major features - adjustable switching frequency up to 200 khz; - optimized for current mode control topology; - inherent feedforward compensation; - soft -start and enable function; - overcurrent protection; - overtemperature protection; - overvoltage protection; - undervoltage lock-out with hysteresis; - low stand-by current; - integrated start-up supply; - automatic burst mode operation in stand-by condition; - internally trimmed bandgap reference. figure 2: block diagram 1 fc00231 v dd osc comp drain source 13 v uvlo logic security latch pwm latch ff ff r/s s q s r1 r2 r3 q oscillator overtemp. detector error amplifier _ + 0.5 v + _ 1.7 m s delay 250 ns blanking current amplifier on/off 0.5v 1 v/a _ + + _ 4.5 v
3/7 application note 1.2 viper100 pin description vdd : this is the low level supply pin of the device. at start up, it delivers 2 ma of charging current. it is also connected to the inverted input of the error amplifier. osc : to be connected to an external r-c network to fix the switching frequency. comp : the control pin of the device. its voltage sets the peak current of the power switch, and it is the output of the error amplifier. as this amplifier is a transconductance one, the compensation network on that pin is simply grounded. drain & source : the two power pins of the device. the source is also the ground reference of the device for compensation and oscillation networks. 2 board features ac input voltage : 90 ~ 265 v ac maximum output power : 50 w dc output voltage / load : vout = + 12v , 4 a operating frequency : 100 khz par. 3 gives the complete schematics of this off line flyback converter. 2.1 feedback loop this demoboard allows the user to choose between primary and secondary regulation. primary regulation is done through the primary auxiliary winding which delivers the low level supply voltage on the vdd pin of the device. this voltage represents also the secondary output voltage, if correctly filtered in order to avoid the spikes at the beginning of each off phase. this mode of running is achieved by putting one strap on jp1 in the "p" position. secondary regulation is made with an optocoupler directly from secondary output voltage. it acts on the "comp" pin, and the auxiliary winding is delivering the low level supply voltage at a lower value than when in primary regulation configuration, thanks to r6. the internal error amplifier is consequently saturated in high state, sourcing a constant current of about 0.5 ma on the "comp" pin. to address this configuration, just put two straps on jp1 in the "s" position. in any case, a strap in "g" position must be always present. 2.2 special operations no limitation has been set on the viper device. this limitation can be implemented on the "comp" pin with a zener or a vbe multiplier, or whatever else able to clamp the voltage on this pin at about 3 v. in this specific case of any clamping the demoboard is able to deliver up to 130w of power, in continuous running. this operation must not last for more than 5 seconds. nevertheless, the demoboard is fully protected against short circuits. this type of condition leads to a burst operation, with peak current of up to 25 a on the output. as the burst duty cycle, is rather low, no risk exists and this situation can be experienced indefinitely. the board withstands the no load condition. pay attention that in primary regulation, the output voltage will rise at about 20 v. secondary regulation provide a better behavior by maintaining the output voltage at about 12 v, and has also the lowest consumption on the main lines : less than 1 watt on a 325 v dc input voltage.
4/7 application note 3 schematics and board layout figure 3: printed board - copper side (scale 1:1) figure 4 : printed board - components side (scale 1:1) 1
5/7 application note figure 5 : demoboard schematics 1 u1 viper100 13v osc comp source drain vdd - + 23 54 1 r8 5.1k r7 3.9k r5 4.7 r6 10 c10 100nf c8 4.7n c7 22uf 16v d7 1n4448 jp1 jumper c9 4.7nf l5 10543330-p1 orega d4 diode zener d2 diode c3 100nf 400v c2 100uf 400v d1 600v, 1a - + l1 inductor l4 inductor l2 b82731-r2801-a30 siemens c1 100nf 400v f1 1.6a r3 33 j1 con2 1 2 r1 3.9k r2 3.9k d3 byw81p150 c4 1000uf 16v c5 1000uf 16v r4 2k d6 led d5 bzx55c11v pot1 1k iso1 4n25 j2 con2 1 2 c6 1nf 1kv p s g s
6/7 application note component list (*) l5 was specifically developed from orega (thomson television component france) for this demoboard. (**) l2 is a siemens matsushita component. device pitch (mm) type description c1 15 0,1 m f 400v film c2 10 100 m f 400v electrolitic,high voltage,high temp c3 15 0,1 m f 400v film c4 5 1000 m f 16v electrolitic, low esr c5 5 1000 m f 16v electrolitic, low esr c6 7,5 1nf 400v ceramic high voltage - classy c7 2 22 m f 16v electrolitic c8 5 4,7nf film,wyma c9 5 4.7nf ceramic c10 5 100nf ceramic d1 8x5 1a/600v dil diodes bridge d2 9 byt11-400 d3 5 byw81/100 d4 9 bzw50-180 d5 7 bzx55c10 zener d6 4 green led d7 7 1n4448 f1 23 2a fuse iso1 5x8 4n25 j1 5 2contacts screw pcb connector j2 5 2contacts screw pcb connector l1 5 100uh inductor 1a rated l2 (*) b82731-r2801-a30 (**) l4 5 100uh inductor 1a rated pot1 4+3 1k w pot 3/4 turn,horizontal,miniature r1 10 3.9 k w 0,25 w r2 10 3.9 k w 0,25 w r3 7,5 33 w ntc lcc r4 10 2 k w 0,25 w r5 10 4.7 k w 0,25 w r6 10 10 w 0,25 w r7 10 3,9 k w 0,25 w r8 10 5,1 k w 0,25 w l5 (*) orega 10543330-pi (*) 1
7/7 application note information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the co nsequences 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 p ublication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectron ics products are not authorized for use as critical components in life support devices or systems without express written approval of stmicr oelectronics. the st logo is a registered trademark of stmicroelectronics ? 1998 stmicroelectronics - printed in italy- all rights reserved. stmicroelectronics group of companies australia - brazil - canada - china - france - germany - italy - japan - korea - malaysia - malta - mexico - morocco - the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. http://www.st.com
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