New topic, similar subject, cause the original one was getting messy. Anyway, this IS a new topic, since there is no longer a question. But additional comments welcomed.
A poster named Spehro Pefhany had questions about the snubber diodes I had across the primary. I had them there to keep the spikes off the driver FET, and when I removed them the transient voltages shot up to
150v. But when a resonating capacitor was placed across the primary, BINGO, spikes gone and the output of the doubler went to 18 volts! (1.8k load)This was with those pair of "C" iron cores. I went back to my air cores, and also to a single-ended driver on the primary. Replacing the load with 820 ohms I now get 6.9v out of the doubler, more than enough to do what I need. (Need 25mw, got 60mw) Also, the primary average DC current is a respectable 50ma vs the 400ma I was seeing before.
The frequency for max output is 44KHz, and is somewhat critical. Output falls fairly sharply as the f goes down, and drops at a much lower rate as the f goes up. This could be a bear for manufacturing, but I have a way around that. I plan to monitor the voltage on a 5-to-10 ohm resistor in the source leg of the driver FET with the A/D of my micro (It can do a 10-bit conversion in 3.5uS). At power up I'll do a frequency sweep of about 40 to 48KHz while monitoring the current through the FET during its on time. I see on a scope that the peak current coincides with resonance. That will be the f it will use, no tuning required.
Picture of the schematic & 2 coils is at: