how to step up voltage from the charging capacitor - Page 1
Forum section: electronics / beginners

author: nady
author_rank: Newbie
timestamp: February 29, 2012, 06:17:44 am
content: hi...i'm doing my project about harvest energy form the vibration.Using supercapacitor 0.22F, i can charge the voltage up to 2V to switch on the LED..My question is how i can construct a circuit that can step up the voltage up to 5V so that it can be used to operate the pic or zigbee

author: Rerouter
author_rank: Super Contributor
timestamp: February 29, 2012, 07:05:11 am
content: more details please, you never mentioned how your capturing energy from the vibrations, what kind of energy it arrives at, nor posted a schematic,i am going to take a guess that the energy input appears like a sine wave? if so you can use 2 diodes to double the voltage, but yeah you wont get as much current,http://www.radio-electronics.com/info/circuits/diode_voltage_multiplier/diode_volt_mult.phpin this example, if it is sinesoidal, ignore the transformer,

author: nady
author_rank: Newbie
timestamp: February 29, 2012, 08:29:00 am
content: I use piezoelectric to capture the kinetic energy from vibration..Actually this is Car engine vibration based Micro-power generator project but the generator will be test in lab with vibrator as a simulation to the car engine.I use function generator to produce the vibration. Then piezoelectric will capture the kinetic energy from the vibration.yes..the energy from the vibration in sine wave so, i use full-wave bridge rectifier to convert AC to DC..Supercapacitor 0.22F used to store the energy. This electrical energy for powering low power electronic system such as wireless sensor node. So, i need to step up the voltage at least 5 volt to operate the pic or 3.3V to operate the zigbee

author: Psi
author_rank: Super Contributor
timestamp: February 29, 2012, 10:01:30 am
content: If it's AC you could use a diode+capacitor multiplier to get a higher voltage.http://en.wikipedia.org/wiki/Voltage_multiplierhttp://www.creative-science.org.uk/multipliers.htmlHowever, depending on the diodes used, the efficiency maybe bad because the voltages are quite low and you have to get past the diode forward voltage drop.You'd definitely want to use diodes with an ultra low drop (0.1V-0.3V).Then it wouldn't be too bad, a three stage multiplier would only lose 0.3-0.9VDiodes with a 0.1-0.2v forward voltage typically only handle 30-100mA at under 20V but that shouldn't be a problem for your application.You may not actually need it though, some micro controllers will run on 0.8V, so 2V might be all you need.

author: bfritz
author_rank: Regular Contributor
timestamp: February 29, 2012, 03:06:45 pm
content: Nady,I think many here may have misunderstood the function of your device. So I will attempt to clarify how I see it working... Correct me if I'm wrong.You use the piezo transducer, to charge up the capacitor (0.22F). From the size of the cap, you have a great deal of energy at 2V assuming a 0.22F capacitor. I assume you need the micro to run, even if the car engine is not vibrating, so using a tripler, or some other scheme using the AC from the piezo does not meet your goals, as you need power even when the engine is not vibrating.I would suggest taking the output from the capacitor, and use a Boost Converter stage. Boost converters can be made quite efficiently. Since efficiency is likely an important requirment, look for a Synchronous Boost Converter design. The following Wikipedia article is a decent example of a standard Boost Converter. A synchronous design will replace the diode with a switch, usually a MOSFET, to reduce power loss.http://en.wikipedia.org/wiki/Boost_converterThere are many parts based on varying input voltages and output currents for synchronous boost converters. TI, National and many others will have parts aimed at your needs. They will do a great deal internally to keep efficiency, so I would start your search there.Good Luck!

author: T4P
author_rank: Super Contributor
timestamp: February 29, 2012, 06:25:48 pm
content: Quote from: bfritz on February 29, 2012, 03:06:45 pmOne should think of it as a switching step up supply , but it uses inductors to store energy and release it later , not transformers to transform .A Mosfet is used to switch the frequency to a certain KHz then dump it through the inductors at a set frequency then filter it .

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 29, 2012, 07:33:09 pm
content: Depending on what you are trying to do, I would look at running a Micro from a 1.8V supply. You can run an ATMega328 at 1.8V up to 4 Mhz. I believe PICs are similar. However, if you are trying to interface with a third party component, then that is limited without boosting the voltage.If you can get all circuitry at 1.8V, then you are going to run longer and be more simple of a solution.

author: IanB
author_rank: Super Contributor
timestamp: February 29, 2012, 08:36:17 pm
content: Stepping up to 5 V from a 2 V capacitor is going to be challenging. Capacitors drop in voltage as they discharge, so the input voltage could be somewhere in the 1-2 V range. If the input voltage were to be 1 V then the step up to 5 V would be a 5:1 ratio, and that starts to get difficult for a boost converter to do efficiently.What others have said about trying to find devices that can operate at lower voltages like 1.8 V is a good idea.

author: Psi
author_rank: Super Contributor
timestamp: February 29, 2012, 11:46:52 pm
content: Quote from: bfritz on February 29, 2012, 03:06:45 pmCouldn't he use the tripler to charge up his 0.22F cap to 6V ?Might need an extra diode but the charge should stay there when the pulses stop.But I agree with what others have said, it's best to find a micro that can run on his current 2V supply.It will be more efficient and give him a longer runtime.Not only because of losses in a multiplier but because a 0.8-1.8v micro will consume less power than a 5v one.He could also use a larger capacitor, 0.22F is still pretty small.jaycar for example have a 22F 2.5V cap for AUD$16http://www.jaycar.com.au/productView.asp?ID=RE6702

author: T4P
author_rank: Super Contributor
timestamp: March 01, 2012, 04:49:17 pm
content: Quote from: Psi on February 29, 2012, 11:46:52 pmThen only then , is it decent . 0.22F is nothing much really .