Re: convert a negative and positive square wave to be only positive.


<overgeo@xxxxxxxxx> wrote in message
news:1153349435.543099.99620@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi, thanks for all your fast and good answer, the output that i have to
drive is an optocoupler the square wave is the signal control for an
igbt finally i have done this,
http://img65.imageshack.us/img65/9913/dibujovt1.jpg, from the
comparator i got a square wave with two values 0, and -15V, and after
i use a transistor to proportionate enough current for the optocoupler,
after the transistor there is a wire that goes to one optocoupler, and
the other wire goes to another transistor to invert the signal and
finally to the other optocoupler.

The circuit in orcad works, but i cant understand a couple of things,
when i connect the comparator to the transistor i got a square with two
values (0, -15), but if a connect the comparator to a resistor and the
resistor to ground i get a square wave but the values are (15V,-15V),
can anyone explain me this? and the other thing, is why i get an invert
output from the transistor. And finally i want to use a fast transistor
and a fast comparator, can anyone recommend to me one?, agian thanks :).


When Q1's base was at +15v, the transistor was on and the collector was
pulled
to ground less Vce (sat). When the base was at -15v, the transistor was off
so the
collector is pulled to +15v by R29.



.

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