Transformer vs. Boost Converter

Discussion in 'General Electronics Chat' started by Hurt_it_Circuit, Jul 16, 2014.

  1. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    Hi, Everyone

    I have to boost a small DC voltage (140mV) to at least 1.5V. From my understanding is that this can be done with a transformer or a boost converter. What is the advantage of using one over the other?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Don't know of any circuit that will operate from 140mV.
     
  3. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    It's coming from a thermoelectric generator. Basically, 140mV is my battery.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a circuit to do this would take more power than it produced. how about series connecting several thermo generators?
     
  5. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    Connecting them in series would increase the voltage a little but it would also increase the resistance which is undesired. With such a small voltage realistically how high of a DC output do you think is possible?
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    Go back to what was mentioned earlier. If there is no circuit that can operate from 140 mV to produce a higher voltage then the answer is that 140 mV is as high as you can go. However I did find the following reference in the wiki on the Joule thief circuit.

    US Patent 4,734,658 [2] describes a low voltage driven oscillator circuit, capable of operating from as little as 0.1 volts. This is a far lower voltage than that at which the Joule Thief will operate. This is achieved by using a JFET, which does not require the forward biasing of a PN junction for its operation, because it is used in the depletion mode. In other words, the drain–source already conducts, even when no bias voltage is applied. The '658 patent is intended for use with thermoelectric power sources, which are inherently low voltage devices.

    "Low Voltage Driven Oscillator Circuit", www.google.com/patents, retrieved 20 March, 2012, filed 14 aug 1987
    http://www.google.com/patents/US4734658
     
    Last edited: Jul 16, 2014
  7. john_doe01

    New Member

    Nov 27, 2011
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    Im not sure how it would work for this application but in general transformers are not as efficient as boost converters
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
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    actually you could do it, but not as a power source. a 555 turning a relay on and off driving a transformer stepping up the voltage choppers used to be used in instrumentation to step up low voltages. there used to be thermoelectric generators to power transistor radios advertised in popular electronics and such, for third world countries without power. ran 9 volt radios, the resistance isnt too high it depends on the size of the thermo elements, not all are twisted wires.
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    Yes, but there aren't any boost converters that run from 140 mV
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Transformers work with AC, not a DC input!
     
    Metalmann likes this.
  11. ronv

    AAC Fanatic!

    Nov 12, 2008
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  12. Papabravo

    Expert

    Feb 24, 2006
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    Did you look at the JFET circuit in the link I gave you?
     
  13. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I tried simulating the jfet circuit in that link but couldn't get it to work. Anyone had any success with a sim?
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    It doesn't have to run from 140mV, it can run from the 1.5v output. :)

    Many commercial boost systems are "bootstrapped" so the control electronics run from the output voltage.

    The only issue is the intitial startup, but if the output is connected to a battery that is not a problem.
     
  15. RichardO

    Well-Known Member

    May 4, 2013
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    This may not be true. If I read the data sheet correctly, this part will run on as little as 50 mV!

    http://www.linear.com/product/LTC3108
     
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