1/5 april 2004 AN442 application note triac & microcontrollers: the easy connection rev. 2 introduction the aim of this note is to show how to connect an st triac and an st microcontroller. conventional solution for many years the triac has been used to switch load on the ac mains and thanks to the low cost of mi- crocontrollers (c) this solution is widely used in the appliance market. all the system use a buffer transistor between the outpu t port of the microcontro ller and the triac as shown in the figure 1. figure 1. drive in the 1st and 4th quadrants because of the low sensivity of the triac in the 4th qua drant this type of drive is often unpractical, and is replaced by the topology of the figure 2. figure 2. conventional drive in the 2nd and 3rd quadrants to save cost, manufacturers want to use fewer and fewer components and of course want to remove the buffer transistor, but a problem arises. line i g c +v dd 0v line +v dd 0v g a2 i g a1 c
AN442 application note 2/5 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. new st solution two parameters have been improved: ? the sensitivity of the triacs. ? the output capability of the microcon trollers in terms of sunk current. a microcontroller is now able to drive one standard triac or several sensitive triacs, without buffer transis- tors (see figure 3). figure 3. an easy connection! table 1 shows the output capabilit y of a range of controllers a nd the sensitivity of the triacs. table 1. triac and microcontroller characteristics microcontrollers & output capabilities triac sensitivity gate parameters connection st621x series st622x series i ol = 20ma at v ol = 1.3v i vss =100ma t & tw series tx05 series i gt = 5ma v g =1.5v at i g = 10ma 1 port/triac s & sw series tx10 series i gt = 10ma v g =1.5v at i g = 20ma 1 port/triac c series i gt = 25ma v g =1.5v at i g = 50ma 2 ports in parallel/triac cw series i gt = 35ma v g = 2v at i g = 70ma 3 ports in parallel/triac b & bw series i gt = 50ma v g = 2v at i g = 100ma 4 ports in parallel/triac line g a2 a1 0v +v dd i g st c st triac v g v ol r g
3/5 AN442 application note example: for +5v supply voltage and a logic level triac with i gt = 10 ma, we have: 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 ? ? v ol ? i g ----------------------------------------- - =
AN442 application note 4/5 revision history table 2. revision history date revision description of changes may-1992 1 first issue 5-apr-2004 2 stylesheet updat e. no content change.
5/5 AN442 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 result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specifications mentioned in this publicati on are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectronics prod ucts are not authorized for use as critical components in life support devices or systems without express written approval of stmicroelectro nics. the st logo is a registered trademark of stmicroelectronics. all other names are the property of their respective owners ? 2004 stmicroelectronics - all rights reserved stmicroelectronics group of companies australia - belgium - brazil - canada - china - czech republic - finland - france - germany - hong kong - india - israel - ital y - japan - malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - united states www.st.com
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