Powering Up Ls7631 At Maximum Intensity

 The LS7631 LS7632 will normally power up in the Off condition
when AC power is first applied or when there is an AC power
interruption  of  at  least  a  second  or more  (the  exact  timing  is
determined by the value of certain application circuit component
values). It is possible to force the LS7631 to power up at maxi-
mum intensity by adding a resistor (R9) and capacitor (C7) to the
application  schematic  shown  in  Figure  6  of  the  LS7631 data
sheet. Minor component value changes are required for some
other R and C components (see bolded components below).
The C7 capacitior produces a short activation at the EXT input
when AC power turns on. This short activation forces the
LS7631 to produce Triac Gate pulses corresponding to maxi-
mum intensity. The R9 resistor is used to quickly discharge the
DC  power  supply  holding  capacitor, C5,  when  AC  power  is
interrupted. This action ensures that the LS7631 under goes a
Power-On-Reset (POR) so that it is set up to react correctly
when AC power is restored.
The schematic shown in this Application Note will work for all
AC  power  interruptions  that  are  greater  than  approximately
350ms in duration. Shorter AC power interruptions will cause
the LS7631 to power up in the Off conditon.
June 2003   
T = Q4004L4 Typical Triac
T = Q5003L4 Typical Triac
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Powering Up Ls7631 At Maximum Intensity application circuits
Powering Up Ls7631 At Maximum Intensity application circuits



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