[Ronja] Is an opamp oscillator reliable?

[Thomas Egenhofer]

> Subject: [Ronja] Is an opamp oscillator reliable?
> To: Twibright Ronja <ronja at lists.pointless.net>
> Message-ID: <5593315.1226478772490.JavaMail.root at viefep11.chello.at>
> Content-Type: text/plain; charset=utf-8
> 
> I want to build an opamp multivibrator to power the onboard 48V generator. A circuit like 
> http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/square.html
> 
> However I have a feeling that the Barkhausen criterion is not met anywhere. The feedback with capacitor has to have 180 degree phase for Barkhausen to be met. This can never happen because the low pass filter has phase limiting to 0 for low frequencies and 90 for high frequencies. However intuitively I understand how it's supposed to work.
> 
> How can this circuit work then? Any idea? Is this circuitreliable at all, then?
> 
> I would like to avoid circuits which fail under certain temperature, supply voltage,
> or component tolerance for some people and work for others.

as far as i know those things work perfectly fine. their frequency is
not very stable and can variate by several percent. same with the duty
cycle. but it keeps working as such as long as the OP-amp is not broken
and input voltage is present. you could also use 74hc14 if you use 5V
input voltage.

if you are in need of a higher supply-voltage take a look at some
"single-use-cameras with flash" they use only a single transistor, a
coil , diode and cap and they reach 200V without problems. some sort of
self-oszillating circuit.but op-amp&cascade is more reliable than
flash-thing-step-up.

slightly off-topic: but it looks like pitch-black-analog-movie material
can make some quite good IR-pass filters. since they usualy are 35mm
square they could be placed quite easy in front of the receiver diodes
for IR-based systems.
looks like color-dia-film material works best. have no numbers on the
filtering itself. but might be intresting for people with
daylight-problems.