Electronics > Beginners
Using varistor instead of pot. to autom. adjust res. in joule-thief for bat.life
JS:
I don't know the parameters of your circuit, but at such low voltage is quite hard to work, even worse without knowing what is actually happening.
The bateroo will keep a constant voltage at the output, you place a resistor and your working conditions are constant till your battery is depleted.
Now, I think you are over engineering this, if it works just fine with a resistor you might be facing a headache that doesn't worth for some extra battery life that doesn't worth it.
Now, I guess the jfet and single resistor won't cut it, not enough voltage to play around with. Another option, jfet, gate tied to ground (battery -), other two terminals to the battery + and anode of the LED. Find a suitable LED which makes a current that make sense at the voltage ranges of the battery. Next improvement, Si diode from V+ (or LED anode) to gate, resistor from there to ground. Now you have a more constant current with the varing V+. Finding the right jfet is the tricky part here.
JS
Distelzombie:
--- Quote from: JS on July 06, 2018, 01:22:16 am ---I don't know the parameters of your circuit, but at such low voltage is quite hard to work, even worse without knowing what is actually happening.
The bateroo will keep a constant voltage at the output, you place a resistor and your working conditions are constant till your battery is depleted.
Now, I think you are over engineering this, if it works just fine with a resistor you might be facing a headache that doesn't worth for some extra battery life that doesn't worth it.
Now, I guess the jfet and single resistor won't cut it, not enough voltage to play around with. Another option, jfet, gate tied to ground (battery -), other two terminals to the battery + and anode of the LED. Find a suitable LED which makes a current that make sense at the voltage ranges of the battery. Next improvement, Si diode from V+ (or LED anode) to gate, resistor from there to ground. Now you have a more constant current with the varing V+. Finding the right jfet is the tricky part here.
JS
--- End quote ---
hi thanks for you answer :)
Find a LED that makes a suitable current? What do you mean? A second led?
What do I search for in case of the JFET? I mean, what property do I have to look out for? And HOW do I look for it?
Also, P or N channel? xD
XD sorry it's like all the possible questions. XD
JS:
it seems like you already have an LED, I'm talking about the jfet.
You need a jfet that with ~-0.5V at the gate you get the desired current. Look at the Id/Vgs plots.
JS
mmagin:
If you're willing to use a proprietary ICs, there are a number of constant current output boost converters intended for running off a single cell. e.g. https://www.diodes.com/products/power-management/led-drivers/low-voltage-dc-dc-led-drivers/part/ZXSC300
Distelzombie:
I finally found the picture or the schematic I drew. (And roughly simulated) It's attached.
The resistor in the picture is where the pot is. Also there is a second transistor in parallel with the one in the picture. This one is a different type and it's glued with thermal paste to the one in the schematic. I'm not sure if the paste was necessary, but I figured, since they sit flat-face to flat-face (ones pins are mirrored since diff. type) on the board, I might as well couple them thermally.
I can't connect anything directly to the LED. It would probably stop oscillation. So it has to be in place of the resistor.
I assume I also can't use the Batteroo or Batterizer. I guess they don't put out flat DC and would interfere, or they just ruin the efficiency. But I'll see where I can get one.
@JS does it even matter if it is P or N channel? I take a look around, but the Ig Vgs or Vds plots are with negative current. Does that matter? Why is it negative?
@mmagin Hm. Oh: "The circuit generates constant current pulses" nope, not gonna work, I think. (How is that constant xD)
I'll try to find a JFET and one of these batterizeroos if they don't cost too much.
Thank you very much so far :)
If you have more ideas now that you have the schematic, please tell me. :)
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