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Need to Step Up Low Voltage

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VSnyder

New Member
I have a fuel cell that produces between .4 and .9 VDC, with current increasing as voltage decreases, max current of 2 A. This .4 volt, 2 ampere condition is the most powerful. I would like to use the fuel cell to drive a motor, let's say 6 V. Is there any way to step .4 V to around 6 V? Is there some way I could turn the steady signal into a wave, without using semiconductors (so that I can avoid the .6 V voltage drop) so that I can step up the voltage with a transformer? Thank you!

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laroche73

New Member
low voltage converters

You may want to look at some of the robotic sites (BEAM), it's a similar situation with solar cell powered motors.
This site has a few solar powered motors that might be useful for ideas:

http://www.solarbotics.net/library/circuits/se_t1_gbse.html

Can you run two of the fuel cells in series? You'll have more luck finding a conversion solution with a 0.8V minimum than with 0.4V. I recently did a similar search with solar cells in mind, and came across a nice line of LED drivers made by Zetex. The ZXSC3xx series will work off input voltages as low as 0.8V. I sent you a PDF of the datasheet.

http://www.zetex.com/frame.asp?page=http://www.zetex.com/3.0/a1-7b.asp?link=spotlight

both the Zetex parts and the 1381 mentioned in the first link can be found at digi-key.
 

bmcculla

New Member
You could build a DC-DC Step Up or Boost converter. THe LM3488 looks like a nice one for a good price. A DC-DC converter switches current through an inductor to generate an output voltage. Thay can be up to ~90% efficient and because they use a feedback loop to keep the output voltage steady you dont have to worry about the .7V drop you are talking about.

Brent
 

VSnyder

New Member
Looks to me like the lowest input voltage I can use is .5 V with a synchronous boost converter, which has a maximum power output of half a watt. I was hoping for some simple way to use just a few capacitors or something to vary the signal (wave or pulses), so that I could use a transformer, which would put out all the power I put in. (As you can probably tell, I really don't know much about electronics.) If anyone has anyone suggestions, I would love to hear them. Otherwise, I'll go with the synchronous boost converter. Thank you for all the help, everyone!!!!!

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laroche73

New Member
low voltage dc-dc conversion

What synchronous boost converter IC did you find that can start up and run off of 0.5V? Just curious.
 

VSnyder

New Member
Search for "synchronous boost converter" at www.digikey.com, and you'll see the list I've been looking at. Several claim to operate down to .5 V--not sure about the start-up, though....
 

laroche73

New Member
start-up voltage

The start-up voltage is usually higher than the minimum operating voltage. For the LTC3400, the worst case startup voltage is 1V (0.85V typ), and the worst case operating voltage is 0.65V (0.5V typ) @ 25C.

The LTC3423 will work off input voltages as low as 0.5V, but needs a separate supply of at least 2.7V to operate its internal circuitry.
 

VSnyder

New Member
I suppose I could use that IC that requires a seperate power source for its internal circuitry, and power it with a watch battery. Am I correct in assuming that the more current I put into this IC, the more I'll get out?

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Roff

Well-Known Member
VSnyder said:
I suppose I could use that IC that requires a seperate power source for its internal circuitry, and power it with a watch battery. Am I correct in assuming that the more current I put into this IC, the more I'll get out?

[email protected]
You could power it from a rechargeable battery that is trickle charged by the output of your converter. Or, if you could start it on battery power then automatically switch over to powering it from the output with a diode OR as soon as the output comes up.
 

laroche73

New Member

thekingkisna

New Member
equivalent to 1381

can anyone suggest an equivalent to 1381... I asked the electronics storeguy and he gave me LM336 Z25. my circuit which is a beam solar photopopper. isnt working. can anyone suggest a site which gives equivalents or let me know if lm336z25 is really a good subsititute for 1381. search for 1381 solar engine, and thats the one that i m trying to make.

thanks.
 

Hero999

Banned
Surely those converters don't require much current to operate the control circuitry which you can run off a couple of alkaline batteries.
 

thekingkisna

New Member
hey hero.. was that to me??? is LM336 an equivalent to 1381.actually me gotta finish the project in next 12 hrs.. sosorta in a hurry
 

audioguru

Well-Known Member
Most Helpful Member
A 1381 is a voltage trigger device. An LM336 is a completely different animal, it is a shunt adjustable 2.5V voltage reference.
 

Hero999

Banned
Here's my idea anyway.

Use a rechargable NiMH battery to power the IC, this will be charged when the power is turned on. The IC uses so little power that a pair of 2Ah cells should last years. If you want to save even more power then you can pull the shutdown pin high to turn the supply off but it probably itsn't worth it unless it won't be used for a year or two.

This is just a quick modification I've made to a circuit on the datasheet, you'll need to reclaculated the resistor values to give the voltage you desire..

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1030
 

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