With this circuit: http://www.interq.or.jp/japan/se-inoue/e_ckt17.htm The output voltage should normally swing between -15V and +15V, or whatever your power supply rails to the Op-amps are. How would one modify the circuit so that the sawtooth waveform swings between 0V and the positive supply rail voltage? Thanks.
Well if you are using a QUAD op-amp IC, its easy- You add a SUMMING amplifer with a gain of 1/2 on the output, have your sawtooth on one summing input, and an offset voltage of +15V (or whatever the saturation voltage is) on the other summing input. Thats my initial reaction.
Just use a virtual earth at half the supply (centre-tap of two equal resistors across the supply) onto pins 3 & 6 and the opamp negative to ground. In practise you can't go rail-to-rail, most op-amps can only swing to about 1.5V from a rail, and if you exceed that the system locks up - the ramping voltage can never reach the changeover point set on the comparator. Hence his comment, "Also, to work in the oscillation, the condition of R3>R4 is necessary. However, when making the value of R4 small compared with R3, the output voltage becomes small." Nice circuit, might come in one day.
Purely out of interest, heres what I get when I simulate that circuit: (O-scope is AC coupled) Any ideas what would make that spike at the peak occur? I'm guessing its to do with the diodes, as thats the only thing that differs to the original schematic.
Could be, audiophiles claim to be able to tell one diode from another in PSU circuits, and go for soft-recovery types that minimise ringing when they switch and small suppression capacitors or snubbers across them. A good simulator (and real-life trace) may show that. What are you using?
Proteus ARES. Which I suspect uses ProSpice. O-T: The demo of this is extremely good, and you can simulate any circuit as i've shown. You just can't save. Which is fair enough in my view.
Hey Cpemma, what spice software did you use to display that? I'm looking for a basic easy to use Spice package that can do graphical layout and basic analog simulation like this, that's freely available, even if it's only a trial version. Any suggestions?? Thanks.
Circuitmaker Student, it's been abandoned by Microde's new owners but was freeware and it's available here along with a bit of a tutorial.
