application note td310 used in a voltage quadrupler AN854/0299 by r. liou ? the td310 is a triple mos or igbt driver which integrates all functions suited for compact and highly secure driving such as adjustable under voltage lockout feature (uvlo), sense compara- tor with alarm output and automatic shutdown, independent operational amplifier, enable pin, and global standby mode (e.g.: for portable applica- tions). the following describes how to generate a dc voltage 4 times higher than the supply voltage of the td310. this voltage may be used as a 2.5w/60v dc supply. principle please refer to figure 1. the buffer n1 is used as an oscillator. the total swing of the oscillation is shifted of +vcc due to the couple diode-capacitor d1,c1 (the real signal shift is +vcc-0.6v due to the diode voltage drop). the couples d2,c2 and d3,c3 also shift this signal of +vcc each. due to the inverting function of each buffer, the maximum swing is appled at each oscillation cycle across each capacitor, ensuring maximum effi- ciency. the couple d4,c4, where c4 is a tank capacitor smooths the dc voltage which reaches approxi- mately 4 times vcc. figure 1 shows the voltage quadrupler application schematic, and figure 2 shows the resulting traces when vcc=15v: . trace 1 : buffer n1 output (oscillator) . trace 2 : tank capacitor c4 output (dc voltage) introduction figure 1 figure 2 1/2
information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result f rom its use. no license is granted by implication or otherwise under any patent or patent rights of stmi croelectronics. specifications mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectronics products are not authorized for use as critical components in life support devices or s ystems without express written approval of stmicroelectronics. ? the st logo is a trademark of stmicroelectronics ? 1999 stmicroelectronics C printed in italy C all rights reserved stmi croelectronics group of companies australia - brazil - c anada - china - france - germany - i taly - japan - korea - malay sia - malta - mexico - morocco the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. ? http://www.st.com design considerations to each triplet of capacitors c1, c2, c3 corre- sponds an optimal frequency of oscillation of the buffer 1. the traces shown on figure 2 have been realised with c1=c2=c3=1 m f, at vcc=15v and 100khz. best efficiency is obtained with 50% oscillator duty cycle the voltage across the tank capacitor c4 cannot exceed 4xvcc - 4xvd (diode voltage drop) figure 3 shows the voltage drop across the tank capacitor c4 (10 m f) when a 1kw load is con- nected. the power dissipated in the load is: . u2/r = 522/103 = 2.7w notes as the td310 can be supplied under a very wide supply voltage range, a 20v supply is achievable from a 5v supply. the enable pin and standby mode are still avail- able, as well as a comparator and an operational amplifier (eg: post regulation). the same principle, using only two inverters can be used to make an nxvcc dc voltage supply. figure 3 application note 2/2
|
