Single Coil Two Transistor Boost Circuits

[MarkE]

Oh, then you will want to add a bootstrap section.

[TinselKoala]

Unfortunately the 2n7000 mini-mosfet has too high a Rdss value and too high gate threshold voltage to be much fun in this circuit. I use them frequently for other purposes but I've never been able to get satisfactory performance from JT/boost oscillator circuits operating at low voltages using 2n7000.  They make excellent LED ring oscillators though, and I use them in inverter-splitter stages for my old TinselKoil 2.0 494-based SSTC driver.

[Farmhand]

Those NCP1400ASN45T1 parts are definitely on the list for next order, I can use one of those immediately. And some of those DMG1012 mosfets as well.

Tinsel, I hear ya, I got the MPSA18's for this circuit because I see you guys use them and looked up the data sheet and it looked good. I got the 2N7000's for the secondary circuit which runs from the first one.

The idea is the VLV (Very Low Voltage) circuit runs from a depleted 1.5 volt cell and boosts the voltage to about 3 to 5 volts, so then a second circuit can boost the voltage further, to maybe 10 to 15 volts. Then it can dump energy from the charged capacitor to a suitable battery using another mosfet or store it at a higher voltage till night so as to run a string of LED's better.

I could use a low power micro for the second circuit. But.... This is fun, oddly fixating. Learning a lot as well.

The second circuit I have now is a CD4049 oscillator and a MPSA06 NPN with the variable "ringy" coil you commented on, it can run from a 25 Farad capacitor initially charged to 5.3 volts and I run it down to 2.5 volts, it power's 4 x 5 mm LED's with 10.75 volts across them And 1.1 mA of current for about 4 hours. It's useful as a light for sure. Just shining directly upwards it's bright enough for me to see to get up in the night and not too bright to bother me.

I plan to upgrade that second stage as well to use the 2N7000 instead of the NPN, And maybe use a different CMOS chip for the oscillator. 

The VLV circuit is to get the 5 volts onto or "into" the 25 Farad capacitor. 

..

[Farmhand]

Can someone tell me if this circuit "First drawing" looks like it would work ? So if there is a problem I can edit the drawing.

Second drawing has a drawing mistake as well (the capacitor C8 is upside down "might blow up like that", I'm better to draw with a pencil).
It's the circuit I use to drive the LED's from the capacitor.

[MarkE]

With the exception that you need to protect the logic gate in both direcctions, and R9 should be much larger than the largest value of R2, the #1  circuit should work.  However it is not going to run down below about 0.9V.  I would use a BAT54S (they come in variations:  C, S, A) to protect the logic gate.  The base drive for Q1 is a power hog.  This is why I recommended a low threshold voltage MOSFET.  There are even lower threshold devices than the DMG1012 that have good specs.

If you want something that will run down to low input voltages, see my earlier post with the boot strap circuit.