A resistor in series with the capacitor makes the on-time more predictable.
The on-time is controlled by the capacitor and its series resistor.
Just trying to make this circuit more predictable
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
Do you mean something like this-I'm not analog fan, but rather like to live in digital world, so not sure if this change is what you talking about?
![](http://s5.postimg.org/hlk1t4mar/prosmps400k_Hz.jpg)
It could be fun to use only two transistors and by adding some toroid core make simply low power SMPS.
I've found BC557 & BC337 Spice models, so I can try simulate this thing in Spice and try to adjust R11, R12 or remove them if current between PNP and NPN transistors will be limited nice by PNP gain, but it could be nice to find a way to have similar ON/OFF times...
but probably this R13 resistor will create voltage divider with oryginal R10 100k and this oscilator will not work..
Anyway it looked like the only possible way to make C10 capacitor similar RC constants during charge and discharge, or I missed something?
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Lets find it out
![Tweak :-/O](https://www.eevblog.com/forum/Smileys/default/smiliey_cal.gif)