Russell McMahon wrote:
>
> *** Yes! This circuit DOES oscillate as shown ***
>
> Here's a simple RC oscillator that MAY show promise for driving very low
> voltage boost inverters.

> The advantage and potential disadvantage of this circuit is that operation
> is RC time constant controlled, independent of inductor flyback timing. This
> can allow confidence in coil driving and on time etc but care must be taken
> with duty cycle allowed and not driving the inductor long enough to allow it
> to be severely saturated.

> I tried an inductor in place of R4 and while this did produce flyback action
> it was not very satisfactory. More experimentation MAY produce a useable
> design. I wonder what Roman can do with this? :-)


I'm guessing from looking at the circuit that
it wouldn't saturate well ie not a great square
wave in the inductor??

Also the emitter resistor is a similar problem to
the 5v -> 13v converter I posted some time back,
good for oscillation but can be a major problem
when you are trying to run the thing from 1v or
less. ie, if replacing R4 with a boost inductor
what voltage appears across R1 when in the ON
state? You are only going to get inductor to
pass uA at best??

The last circuit I posted has no emitter resistor
and the base resistor was only 120 ohms or so
as this enables it to drive Q1 into hard saturation
even with input voltages of 1v or less.

With your circuit at (say) 50mA ON you would need
R1 to be very low, say 4 ohms, giving 0.2v lost on
R1 and Q2 base at 0.6+0.2 =0.8v only giving 0.2v
across R3 or 60uA available to drive Q2, which
obviously won't saturate Q2!

I think it is really going to need the 3rd transistor
to be a viable SMPS power circuit, and still don't
see any real advantages over my (or Dave Tweed's)
2-tran circuit. :o)
-Roman

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