the aim of this note is to show how to connect an sgs-thomson triac and an sgs-thomson microcontroller. i - conventional solution for many years the triac has been used to switch load on the ac mains and thanks to the low cost of microcontrollers ( m c) this solution is widely used in the appliance market. all the system use a buffer transistor between the output port of the microcontroller and the triac as shown in the figure 1. because of the low sensivity of the triac in the 4th quadrant this type of drive is often unpractical, and is replaced by the topology of the figure 2 : to save cost, manufacturers want to use fewer and fewer components and of course want to remove the buffer transistor, but a problem arises. due to the low output current of the microcontroller, the triac had to be very sensitive and consequently was not able to withstand for example the static dv/dt, and the commutation. ii - new sgs-thomson solution two parameters have been improved : - the sensitivity of the triacs. - the output capability of the microcontrollers in terms of sunk current. a microcontroller is now able to drive one standard triac or several sensitive triacs, without buffer transistors (see figure 3). application note AN442/0592 triac & microcontrollers : the easy connection a ph. rabier figure 1 : drive in the 1st and 4th quadrants. line ig uc +vdd 0v 01phr358 figure 2 : conventional drive in the 2nd and 3rd quadrants. line +vdd 0v g a2 ig a1 uc 02phr358 1/3
figure 4 shows the output capability of a range of controllers and the sensitivity of the triacs. to take into account of the dispersion on r g , v dd and on the temperature variation, we generaly choose about: i g = 2 .i gt (i gt =specified gate trigger current) tp > 20 m s where tp is the pulse duration of gate current. example : for +5v supply voltage and a logic level triac with i gt = 10 ma, we have : r g = v dd - v g - v ol i g where : v dd supply voltagage v ol output low voltage of the microcontroller v g gate - anode 1 voltage at i g with : v dd = +5 v v ol = 1.3 v v g = 1.5 v i g = 20 ma therefore : r g = 110 ohms iii - conclusion use sgs-thomson sensitive triacs driven by an sgs-thomson microcontrollers and remove the buffer transistors. this can be achieved thanks to the high current capability of our microcontrollers which are compatible with our new sensitive triacs (t410, t, tw, s, sw series). furthemore a non sensitive triac can be driven by several output ports in parallel. figure 3 : an easy connection ! line g a2 a1 0v +vdd ig sgs thomson uc sgs thomson triac vg vol rg 03phr358 triac sensitivity t & tw series tx05 series igt=5ma s & sw series tx10 series igt=10ma c series igt=25ma cw series igt=35ma b & bw series igt=50ma 2 ports in parallel/triac 3 ports in parallel/triac 4 ports in parallel/triac 1 port/triac 1 port/triac st621x series st622x series iol=20ma at vol=1.3v ivss=100ma microcontrollers & output capabilities gate parameters vg =1.5v at ig = 10ma vg =1.5v at ig=20ma at ig =50ma vg = 2v at ig =70ma at ig= 100ma connection vg =1.5v vg = 2v figure 4 : triac and microcontroller characteristics. a application note 2/3
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 part ies which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of sgs-thomson microelectronics. specifications ment ioned in this publication are subject to ch ange without notice. this publication supersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support devices or systems with out 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. a application note 3/3
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