Re: Transformer coupling question

Robert Baer wrote:
I have a nice toroid transformer oscillator that works from about 600mV supply and up; very ligit load; made with two transistors, collectors drive CT primary with 10 turns each side and 3 turns feedback to the bases (biased with 4.1K to supply).
The output waveform looks like a square wave but has definite overshoot on each edge and a little droop; did not measure the frequency; the toroids are made with some kind of powder ferrite.

That overshoot and droop is caused by running the magnetization current up till the core saturates and the transistors run out of current gain and come out of saturation. At that moment, since the core is saturating, the turns become poorly coupled and each winding acts like a fairly separate, variable inductor.

Ten turn secondary to a FWB gives about 450mV at 600mV supply, about 1.6V at 1V supply and about 5.5V at 3V supply.
What i want to do is run a common "driving" secondary winding from this toroid oscillator to three or so other toroids (same size and type) that each has ten turn secondaries and that FWB load (1meg, 0.1uF).

Why not run the voltage from the two collectors directly to these other transformers, so that the first transformer acts only as the frequency determining base drive mechanism, instead of also having to do duty as a power transformer?

Do i need to put a resistor in series with that "driving" winding to prevent excessive loading, and is it OK to use one turn for that or better to use ten turns?

(If the cores are all the same) you need to have a higher turns count on the other transformers, so those cores see less volts*seconds per turn and so, do not experience as large a flux swing per half cycle and do not saturate. Then they will not draw a big current spike at the end of each half cycle.
.

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