Single Coil Two Transistor Boost Circuits

[Pirate88179]

Wow does SMD stand for "Super Minute Devices" or "surface mount devices", these things look like fleas stuck to a piece of tape.
I'll need to sharpen my soldering iron point, find some tweezers and solder some pins on one of each part to prototype with. Or maybe I can make some tiny adapters with little bits of circuit board. I've got PCB making gear to make a simple tiny board.
My oh my so tiny.  Will make a compact circuit though.

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I can only solder SMD chips (surface mount devices) using my glasses, and magnifying lens (illuminated) and my Hako super sharp soldering tip.  I have no idea how you heat sink these devices to protect them.  So far, I have not fried any of them but, it is a wonder.  Some of these things I can not see with my bare eyes.  Makes for a compact circuit though.

Bill

[Farmhand]

The only small inductors I coud find right off are about 15 mm high and 10 mm diameter, they measure 1 mH. So I adjusted the circuit to work at a reasonable period for that coil. I have the "on time" screwed back because I'm charging two 3.6v NiMH batteries with one AAA for the supply which started at 1.38 volts so I could see how it runs with a higher input than 1.2 or under and working into a bit of load. I am using an MPSA06 transistor as I still haven't got the mosfet. The resistor R1 can be 20 to 50K, 20K is the setting to get the "on time" in the shot, but it can be more or less of course, on time can be adjustable.

I've got the batteries being charged across the 10 uF output capacitor naturally.

The frequency and width in the shot mean nothing because of the oscillations ect. It's about 46 kHz and around 8 uS on and 13.5 uS off.

Little inductor rings real good, I got two of those from an old PC power supply, less than 1 Ohm resistance.

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[MarkE]

The inductor ring-out is due to discontinuous conduction and parasitic capacitance.  For the most part it is neither here nor there.  It should be fun to see how low you can get the circuit to run.  The dirty trick that you might wish to try is to use a pair of Schottky diodes and a 0.1uF capacitor to form a bootstrap supply for your logic gate.  The Schottky cathodes would be common to your logic gate Vcc.  One anode goes to your battery, the other your output.  The capacitor goes from the cathodes / IC Vcc to ground.  You will have to be careful about exceeding the IC maximum voltage.  An LM4040 has a pretty small minimum current and would work to regulate the output.

[Farmhand]

I've got BAT54C's on the way, in the bag with the mosfets. I think they are the correct one for that bootstrapping. The BAT54S's would be handy as well for protecting the logic gate output of a "drain feedback setup" maybe.

It does seem to be remarkably efficient already and it's on the solderless board with wire everywhere, on a 1 inch square PCB it should be spot on. If it will fit with the output connector and the AAA won't fit on 1 x 1 inch either, oh well. It's capable of a reasonable output with 1.3 volts input and more on time.

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[MarkE]

I've got BAT54C's on the way, in the bag with the mosfets. I think they are the correct one for that bootstrapping. The BAT54S's would be handy as well for protecting the logic gate output of a "drain feedback setup" maybe.

It does seem to be remarkably efficient already and it's on the solderless board with wire everywhere, on a 1 inch square PCB it should be spot on. If it will fit with the output connector and the AAA won't fit on 1 x 1 inch either, oh well. It's capable of a reasonable output with 1.3 volts input and more on time.

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Great.  I am glad you are having fun with the project.