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Registered Member #575
Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263
Robert2 wrote ...
Ok i use only one 555 with out interupter. Use 74hc14 ?
I'm sorry, of course you can use one extra 555 as an interrupter. You can use a 74hc14 based self oscillator to tune up to resonant frequency. You can also use the PLL topology:
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
Well, in fact that 555 version is pretty bad as it uses a pretty scary modulation mode. Instead in case you want an actual open-loop PWM I'd stick to any avalable PWM controller (starting with the good old 494 and carrying on with the new TI chips). If you'd prefer feedback, you can still implement the PWM by making an RC delay circuit after the input trigger. Picked up with a comparator and then combined with the oroginal signal via an AND gate this gives a perfect deadtime via delaying the rising slope (the AND gate makes the falling one remain intact). Using two of those circuits for direct and inverted signals while applying a normalized modulation signal to the comparator negative pin will result in a variable threshold and, therefore, a voltage-controlled PWM.
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sstc + audio modulation
