Hi all,
Remember last project where we described a sawtooth oscillator ?
In the last experiment, we noticed that the slope of the sawtooth wasn’t lineair at all.
This is a natural phenomenon when we charge a capacitor.
We have explained this earlier, look here : Capacitor tester
So, to overcome this, we need to charge the capacitor with a constant current.
A method to use is a Widlar constant current source.
We will use 2 Si PNP transistors T3 & T4.
T4 has its Base and Collector tied together. So the current flowing through the Base and Emitter will be constant.
This current is mirrored to T3 (Bases are tied together), so T3 will charge the capacitor with a constant current.
The rate of charging current is determined by R5 (100 K).
As Michael mentioned, this circuit is build with the modern Silicium transistors and has a negative ground.
The legacy transistors with their build in resistors can’t be used.
Here’s a diagram and setup.
When you look at the Oscilloscope, you’ll notice a perfect lineair slope.
Many greetings
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This topic was modified 3 years, 3 months ago by LectronFan.