i description of the avs 08 : the avs08, is an automatic mains selector to be used in on line smp supply with power up to 200w. it is made of two devices. the avs is compatible with 50 and 60 hz mains frequency and operates on two mains voltage ranges : on range i (110 v rms ) the ac voltage varies from 88 to 132 v and the triac is on : the bridge operates as voltage doubling circuit. on range ii (220 v rms ) the ac voltage varies from 176 v to 276 v and the triac is off : the circuit operates as full wave bridge. ii performance of the avs : the control of the switch is made by the com- parison of the mains voltage (vm on pin 8) with internal threshold voltages (vth and vh on pin 8). this switch modifies automatically the structure of the input diodes bridge in order to keep a same dc voltage range. when mains voltage increases from range i to range ii the triac conduction is completly stopped before one mains period because vm > vth. when mains voltage drops from range ii to range i vm becomes lower than vth - vh. there are two options (v mode on pin 7) : v mode = vdd ; the triac triggering is valided 8 mains periods after power on reset. v mode = vss ; the triac control remains locked to range ii until circuit reset. iii use of the avs : calculation of the oscillator : application note AN391/1090 how to use the avs 08 ? preliminary note 1/5
the oscillator frequency is determined by the mains frequency (50 and 60 hz) and the gate control : its required value must be 45 khz 5%; so the value of components is : c = 100 pf/5% r = 91 kohms/1% the frequency control is made on pin 3. adjustement of the mains mode change : the measure of the mains voltage is made by a detection of the peak value. the change of mains range is made by ad- justement of resistor bridge and we advice : 800 kohms < r1 + r2 < 2 mohms calculation of the change from range i to range ii (on pin 8) : [vth . (r1 + r2)]/(r2 . 2) + vreg / 2= max.rms voltage on range i vreg typ = - 9 v and vth typ = 4.25 v calculation of the change from range ii to range i : [(vth - vh) . (r1 + r2)/r2 . 2] + vreg / 2= min . rms voltage on range ii vreg typ = - 9 v and vh typ = 0.4 v performance of the power on reset : the power on reset permits the charge of the bulk capacitors of the smp supply through soft start circuit. the triac triggering is valided (on range i) after the validation of power on reset (charge of sup- ply capacitor c) and a temporization of 8 mains periods. t delay = delay time between power on and triac triggering td = 0,89 . vreg . r . c/[(v rms . 2/ p ) - r . iss] + 8/f f = mains frequency r = supply resistor = 18 kohms c = supply capacitor = 33 m f v rms = mains voltage iss = quiescent supply current of avs supply of the controller : the structure of the supply regulator is a shunt regulator and its current must be lower than iss max = 25 ma. in order to have a good behavior of the circuit against mains voltage spikes the pin 4 (vdd) of the integrated circuit has to be connected straightly with the a1 of the triac. in same way the supply diode rectifier and r1 have to be con- nected to the diode bridge (see typical applica- tion diagram). triac control : between pin 5 and triac gate there is a resistor in order to limit the gate current; its value is given by the controller supply and triac ; the re- quired value is 390 ohms (5%). thermal rating of triac : the knowlegde of the rms triac current and the current pulse width tp in worst case conditions allows to calculate the losses, pt dissipated by the triac : figure 1 of dc general characteristics of triac gives these losses pt. the external heatsink r th can be also calculated with pt and ambient temperature tamb. tj - tc = r th j-c ac x pt tc - tamb = r th xpt tp = a / 21600 for example : if tp = 2ms and i trms =3a pt = 2w and a =43 tc = 92 c if tj = 100 c r th =21 c/w if tj = 100 c and tamb < 50 c ? application note 2/5
figure 1 of the av08 data sheet designation qte reference observations marque printed circuit resistance resistance resistance resistance resistance diode condensator condensator triac integrated circuit support inverter socket plug 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 4751 r1 r2 r3 r4 r6 d1 c1 c2 ic2 ic1 sw1 sl 3w bl3 1 mohms 1% 18 kohms 1% 91 kohms 1% 9.1 kohms 1w 390 ohms 5% 1n4007 100 pf 5% 33 m f 16v radial avs08cb avs1bcp08 ci 8 pins minidip 3 pins 3 pins sgs-thomson sgs-thomson weidmuller weidmuller annex : avs demo board component list for avs08. example on avs08 : ? application note 3/5
components layout printed circuit layout (copper side) : 1/1 scale products pin out to 220 ab (plastic) dip-8 (plastic) ? application note 4/5
information furnished is believed to be accurate and reliable. however, sgs-thomson microelectronics assumes no responsability for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of sgs-thomson microelectronics. specifica- tions mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information pre- viously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of sgs-thomson microelectronics. ? 1995 sgs-thomson microelectronics - printed in italy - all rights reserved. sgs-thomson microelectronics group of companies australia - brazil - france - germany - hong kong - italy - japan - korea - malaysia - malta - morocco - the netherlands singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. ? application note 5/5
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