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?

 

Don't know of any circuit that will operate from 140mV.

 

It's coming from a thermoelectric generator. Basically, 140mV is my battery.

 

a circuit to do this would take more power than it produced. how about series connecting several thermo generators?

 

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?

 

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

 

Im not sure how it would work for this application but in general transformers are not as efficient as boost converters

 

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.

 

Im not sure how it would work for this application but in general transformers are not as efficient as boost converters

Yes, but there aren't any boost converters that run from 140 mV

 

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 ....

Transformers work with AC, not a DC input!

 

Google energy harvesting IC and you will find some similar to this one:

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/DM00100984.pdf

 

Did you look at the JFET circuit in the link I gave you?

 

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

 

Yes, but there aren't any boost converters that run from 140 mV

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.

 

Yes, but there aren't any boost converters that run from 140 mV

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