I've built the basic test circuit shown in the datasheet for the XR2206, it works ok, but when I'm turning up the supply beyond 10V, the output becomes unstable and the frequency wobbles around.
Yes, it's a half decent bench supply, I've tried adding capacitance on the supply outputs too but makes no difference. I am trying to test it on a breadboard though. I've never seen a similar effect before with any other circuit on my breadboard.
Maybe it is your board layout, Noisy supply maybe? Power leads to thin and long. Poor grounding. Could be a number of things. Are you using a breadboard? If so the breadboard may be causing weird oscillations.
The capacitance between tracks on a breadboard and the long connecting wires (antennas for mains hum) cause many circuits to not work properly. I didn't mention the many intermittent contacts.
Why not quickly design a compact stripboard or pcb layout and SOLDER the connections?
It is the frequency that's jumping around. I've attached scope shots at 10V and 25V.
At 25V the sine has lots of noise. The frequency of both is jumping around on both, although that is hard to see from the scope still.
I'm using a split supply, therefore all the GND points in the diagram go to negative rail, and I use the supply GND instead of the resistor divider near pin 3. (I tried the resistor version on single supply too but same result)
Might be onto something here. With scope between + and - on the supply, the reading is between 12mV and 20mV (15mV typical) RMS which seems quite a lot to me.
When I measure between GND and a rail there's a 250mV 50Hz signal. This drops to 50mV when my circuit is attached, but that still seems like loads!
Might be onto something here. With scope between + and - on the supply, the reading is between 12mV and 20mV (15mV typical) RMS which seems quite a lot to me.
When I measure between GND and a rail there's a 250mV 50Hz signal. This drops to 50mV when my circuit is attached, but that still seems like loads!
The amount of ripple is still the same at 10V input yet everything works fine. It's only turning up the voltage that seems to set it off. Anyway, will try with a pair of 12V batteries and see how that goes!
Ok, so same result even on a battery. It's not the PSU.
I have noticed that if I use a larger timing resistor such as 1M, the problem becomes significantly worse. Unfortunately, using a much smaller resistor does not make it better.
Tried all sorts of combinations or R & C, but can't get it to be better. I've attached a shot of the signal I measure on the timing cap (scope on AC coupling). Seems messy, is that how it should look?