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Author Topic: Single Coil Two Transistor Boost Circuits  (Read 56342 times)

Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #60 on: June 26, 2014, 03:59:45 PM »
Here's a higher resolution shot of the wave form, just need to work out how to make it display more info.

Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #61 on: June 28, 2014, 04:04:12 PM »
Interesting behavior from a circuit on a hand drawn PCB made to take the little logic gates soldered to the adapter's.
The circuit worked as above post shows in normal mode, then when the input capacitor voltage dropped down to about 0.75 volts the
circuit flickered the LED's for a few seconds then they light up even brighter because the circuit was operating at well over 300 kHz in
a odd feedback kind of mode (no ring down). I made a mistake on the hand traced board that I had to fix using a jumper and
stretching my timing caps out. I made the traces so I can solder the SMD mosfet on the back as well I can solder SMD Shottky's on
the back as well if I want later, 1N5819's for now.

Now the real interesting part, it ran for about an hour from a 50 Farad capacitor charged to 1.16 volts even using the MPSA06 transistor.
I ran it down to 0.68 volts and it was still lighting the LED's pretty well but sucking the voltage down on the cap in the higher frequency mode.
Not sure if it will do that with a mosfet.
..
scope shot shows the wave form when the circuit is in the low voltage high frequency mode. I'm only lighting 2 x 5 mm LED's now instead of three.
.

TinselKoala

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Re: Single Coil Two Transistor Boost Circuits
« Reply #62 on: June 28, 2014, 04:33:36 PM »
Here's a higher resolution shot of the wave form, just need to work out how to make it display more info.

You may find this video of use:

http://www.youtube.com/watch?v=9FDmkbCbKP0

Also, you could position your X1-X2 and Y1-Y2 cursors a bit better; at the moment they don't seem to be related to the waveform, you just have them at arbitrary locations on the screen.

I don't know what the Rigol can display in terms of "measurements" or "parameters" that it determines from the waveform itself, especially with a burst oscillator like some of our JTs. You will probably have to do an exploration, like I showed in the video, and also use the cursors in various positions once you have a stable display of an interesting feature of the waveform or pulse train.

Nice work all around though, I'm tempted to build a "twofer" myself.

Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #63 on: June 28, 2014, 05:08:57 PM »
Yeah I just grabbed that picture while I had it there, the communication between the scope and the computer is flakey, so I was
sidetracked  trying to work out why, I was lucky to get that, I think it could be the cable.

I had to order a laser printer online, maybe a week I'll have more stuff to play with, time to install a new motherboard in my desktop
computer. Laptop is a bore to type on. Thanks for the tips. I've cleaned the cable connections so I'll try again. Might work better with Linux or windows 7, this laptop is XP. USB sucks with XP.

Looks like I'll get at least the same 1 hour's run time from the second 50 Farad capacitor. The LED's have about 5.4 volts across them mostly.

Works out to about 22 Joules for an hours run.

TinselKoala

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Re: Single Coil Two Transistor Boost Circuits
« Reply #64 on: June 28, 2014, 05:16:25 PM »
Yah, the LEDs will always act as a kind of voltage regulator, you will rarely get more than the sum of the spec fwd voltages when you measure across the LED stack. But I've got oscillators like this that will work without the LED load being in place (so it's kind of like driving a really really high impedance load). In this case the voltage can go quite a bit higher. You might try putting more LEDs in series as the load and see how high the oscillator will push the voltage. I've also found that the different colors of LEDs behave quite differently. Some have a very sharp "turn on" and others, like these red superbrights I have, seem to "leak" substantial current well before they start glowing visibly, and do glow at lower voltages than blues or whites.
Try four blues in series and see if the voltage goes high enough to light them.



Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #65 on: June 29, 2014, 12:53:39 AM »
I think the transistor is funky, it won't work with 1.25 volts but does work with 1.16 volts, weird. Anyway, when the mosfets arrive I'll do more proper testing, this big PCB is more or less a PCB prototype, I can change stuff pretty easy but much better performance and less jitter than the solderless board. I'm going to increase the frequency, reduce the on time and try a MPSA18 transistor for something to do. I'll try 18 K and 10 K for the timing resistors and the timing capacitance can be 200 pF. Should get it up over 100 kHz and keep oscillator power down, by keeping a small timing capacitance. And hopefully if a higher frequency low voltage mode occurs it will be even higher than 325 kHz but cause a bit less power draw at low voltage. It actually lit the LED's better in the high frequency low voltage mode than in the regular mode. I've got a capacitor across the diode and circuit ground so I've got more or less DC with bumps across the LED's.

..

Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #66 on: June 29, 2014, 02:50:53 AM »
ahah, with higher than 1.2 volts input a 100 Ohms base resistor is required, I think to decouple the transistor base from the logic gates... hmmmm
With a mosfet that is not an issue. The base resistor will probably reduce the rise ad fall times reducing peak voltages and also raise the lowest voltage it will run from.
Not sure I'll have to see. But at least now it will run fine with over 1.3 volts input.

I think it will light up 4 x 5 mm bright white LED's no probs with under 1 volt input. I don't have any blue or other 5 mm LED's.

..

Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #67 on: June 29, 2014, 04:14:00 AM »
PCB Layout needs a redesign, (the PCB layout in post #63 is wrong, below picture is correct). now with the correction made to the traces the
jumper needs to go right around the resistors to the other side of them, so a redesign of the basic layout is in order.
I got confused with upside down parts and stuff. Glad I tested it out with a hand drawn bigger PCB, good to get the finer points ironed out.
..
 

Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #68 on: June 29, 2014, 01:05:36 PM »
With 1 volt it lights up 4 x 5 mm LED's ok as the picture shows anyway. But at 0.8 volts it lights them up less than I would like, and
 the power draw is more as well.
..

Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #69 on: June 30, 2014, 06:28:21 AM »
One thing we can do with circuits that run on low voltage is use home made primary batteries and such contrivances for the power source.

I'm fairly confident I can construct a primary battery that will supply the circuit with enough power to run continuously for as long as the battery lasts,
which could be a long time depending on the size and type. I intend to try several different methods including the bi-metal coil battery.
Building a bi-metal coil battery is not as easy as it sounds so a simpler construction might be the better option for me.
I ordered some magnesium ribbon to experiment with for magnesium-carbon batteries. Going by my experiments zinc/steel-carbon
batteries I think the magnesium-carbon combination will work well enough and be simple enough to be practical.
The challenge come in making one small but with good enough output and long lasting enough to be useful.

For situations where a stationary device needs only a small continuous input or where a device needs higher powers only part of
the time a simple primary battery and circuit to boost it's output into a storage cell of a higher voltage could be useful for long term
very cheap source of power for many things, basically anything that will run from a battery.

So with that in mind I think i want a circuit to boost the initial low power cell output into a battery of 3 to 5 volts and the circuit should
 be regulated so that it stops when the output battery is charged and restarts when the output battery gets used.

This would allow me to charge up capacitor powered torches real fast and without cranking. All I need do is primary battery
maintenance every now and then.

I could use any rechargeable battery or stack of rechargeable batteries for the output battery and simply use capacitors in a couple of torches.

The grid connected commercial equivalent would be a charge station that accepts a couple of torches containing supercapacitors,
when the torch runs low just put it in the "charge station" and its charged in a few seconds or a minute or two. No need to wait for
hours for the torch battery to recharge.

..

Farmhand

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Re: Single Coil Two Transistor Boost Circuits
« Reply #70 on: July 05, 2014, 01:02:05 AM »
MarkE was right, with the little mosfet in the circuit with the logic gate oscillator the switching goes bad at about 1 volt. So to work
at under 1 volt it needs a bootstrap setup.

The printer has arrived so I can get all fixated on designing PCB's for a while. I've got NCP1400 boost chips so I can try one of those
out too.

I made a small carbon - magnesium battery and they seem to work fairly well as compared to a piece of zinc and a piece of carbon
stuck in some dirt. 1.5 volts open circuit on a cell drops to 0.8 under the load of the circuit but charges a 1.5 Farad capacitor pretty quick.
I found that the surface area of the electrodes and the spacing are big factors in the current available, the electrodes can't have too much surface area but they can be too close together with too little resistance between them for the surface area that there is.

The carbon - magnesium battery can be constructed dry then stored and activated by adding water when desired, which could be handy for some situations. eg. hiking, when weight is a concern, dry cells can be carried and water from nature can be added to make the battery active if needed. I think the carbon will last a long time and if the magnesium can be easily replaced then it's a viable source of power for light or to recharge a phone ect.

I made a very dodgy one in a pill bottle, I could have use three times as much magnesium ribbon in it. It gave good current but the
voltage dropped a lot when loaded to 0.8 volts.