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Limited range voltage doubler circuit

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Just got back to the computer. That doesn't looks too bad, I assume the diodes are typical silicon diodes, 1N4003 or similar? I added the diode you mentioned, is that what you were thinking? I see a 15V Zener, what are you using there? I have some 1W 15V Zeners. What transistors are you using, I'm thinking something generic like the 2N2222, I have a raft of those.

Limited Range Voltage Doubler Circuit.jpg
 
You added the diode correctly. D3,4 can be 1N4148, but 1N4003 etc will work. Using schotky's for all would be OK too, and would give a bit more range. Q1 has to be a PMOSFET, with a threshold voltage in the 1 to 1.5 volt range, and an Rds of .1 to .5 ohm. I used what I had, a IRLML5203TR. It has an Rds of .25 ohm at a -3 Vgs. Q2 is pretty much any PNP: 3906,2907,3702,etc. I am using a 1W 15V Zener. The resistor values aren't set in stone either, in fact they are a bit on the high side. D4 was originally a resistor which meant R1 had to be fairly large; they can be scaled down by a factor of 5 to 10 ( going lower would just waste power.) R2,3 set the turn on point for Q2, ( R2/R3 + 1)Vbe, which is meant to be about half of Vz. I used 47 uF for C1,2 but you should use whatever you determined was needed in your setup.
 
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You're right, I didn't look close enough at Q1, didn't notice the extra line, no problem I have some TO-92 P-chan MOSFETs that should work. I also have some 2n2907 transistors.

I suspect that 47uf is too low to generate the 100ma at low voltages needed to power the circuit, I was using 470uf, but I think I can live with around 220uf. I tried it with 100uf and it didn't have the current output at low input voltages to power the load.
 
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